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Hacking my “smart” toothbrush
- compiler-guy 3y agoAt your next dentist appointment: it seems like your toothbrush isn’t getting security updates.
- JohnFen 3y agoSmart toothbrush heads must be in the running for the most needless use of sophisticated electronics.
- barelyauser 3y agoHard to compete against the Bluetooth enabled one-time-use pregnancy test.
- predictabl3 3y ago"But I wouldn't know when to replace my brush-head without this smart toothbrush with it's embedded electronics in a piece of plastic to track on time, contributing to further e-waste in a way that we all know will lead to planned obsolescence the second that Braun decides they need to prop up revenue in a bad year". I mean, we have entire app ecosystems now that are basically just "hey, have some self control and put your phone down", so I'm not sure why this surprises me.
- aio2 3y agoIt's a goddamn fucking toothbrush, no need to have all this stuff.
- dpedu 3y agoI've owned several of these toothbrushes - it's worth pointing out that they work just fine with 3rd party heads with no chips in them. At least, the 2 models I've owned do. Something bizarre I noticed about these Philips toothbrushes is that they fail on a reliable schedule. I owned 3 of the "4100" model and they all failed after exactly 13 months! What's crazier, is that they all failed in the exact same place. There's a metal piece that protrudes outside of the case where the heads attach. Inside the case, this piece clamps to the part that creates the vibrations using a single screw through a cast zinc/nickel block. On _all_ of my brushes, this block cracked right through the screw hole. What's cool is that the vibration motor uses a magnet of similar strength of hard drive magnets, so now I have some nice strong magnets on my refrigerator.
- gerdesj 3y agoI own an IT company in a town (Yeovil, UK) on an acre plot with a roughly four acre plot next door. We have a fair few busy roads adjoining our place - A30 and A37. I have deployed Home Assistant on a laptop with a fair few dongles (Zwave/Zigbee etc) but its built in Bluetooth has noticed loads of toothbrushes - Oral B. I also see lots of some sort of plant auto water thingies and loads of lights. Our office is next to a roundabout that sees at least 30,000 cars a day on one side. I've turned off the car integrations and several others because HA went a bit mad. I see a lot of data that I don't want to without trying and it gets in the way. I do encourage people to stop leaking.
- KevinChen6 3y agoWhat? Has the world become so complicated? In my impression, only toothbrush knowledge has added a micro motor, does it really need to be so only?
- indigoabstract 3y ago"Invalid brush password. Please use the manual mode to brush your teeth."
- treebeard901 3y agoPlease renew your toothbrush service subscription to continue brushing
- dustymcp 3y agoWhat is the point of passwords on your toothbrush again ?
- AquinasCoder 3y agoThis was an enjoyable read. My GE fridge uses RFID for keeping track of when to change the water filter. This isn't really an area I'm familiar with but I'm curious how much I would be able to figure out with the right tools.
- throwway120385 3y agoIn GE's defense, limiting the amount of time you can use a water filter for is probably a good idea considering what the filter media fills up with if you do nothing.
- jerkstate 3y agoThe OEM filters cost like 2-4x what a suitable generic costs. Would have been cheaper for GE to add a software feature to warn you after 6 months and allow you to reset it.
- jerkstate 3y agoThere is a much simpler solution, buy the bypass plug which has the rfid chip in it for about $50, cut a chunk of plastic with the chip off being careful not to harm the antenna, and tape it to the inside of the fridge in the same area. Only downside is you have to use your brain to replace the filter with a compatible one every once in a while, and it says “not filtering” on the front panel when you dispense water or ice.
- roundandround 3y agoI'm curious to see, but I don't think the algorithm for calculating the password from the identifier would be very sophisticated. Assuming they didn't want to add costs to prevent easy retrieval of any secret key from the device, a complex algorithm would be kind of a waste.
- nneonneo 3y agoI mean, even something as simple as `md5("very-long-secret-only-phillips-knows" + uid)[:4]` would be effectively unguessable. Not hard if you have the code for the firmware, but nigh-impossible otherwise.
- netsec_burn 3y agoThe Sonicare app lets you download the latest firmware blob. So all you'd do is intercept it and find the function responsible for generating the password.
- kuroguro 3y agoThe app has the firmware embedded in it (resources/assets/firmware), not sure if it actually downloads a newer one or if it updates with the app. It does seem to be encrypted or compressed somehow tho.
- kuroguro 3y agoIt does seem to be for the more expensive diamondclean series tho I guess the brush checking would be similar. Didn't find any decryption in the APK, it just transfers it as is. Must be hidden inside the firmware as well. I don't think there's any way to get the firmware except dump it from the chip :/
- roundandround 3y agoIf one person has access once and publishes it, the work of setting up a proper md5 was a waste compared to an xor.
- mikestew 3y agoGreat article, the most interesting part of which is that you can lock your self out of your toothbrush head after three wrong password attempts. I didn't dig into the data sheet for the NFC chip very deeply, but I imagine that it's just the default that the chip ships with. Or maybe Philips really wants that $25 for a new toothbrush head. :-) EDIT: nope, not the default. From the data sheet, last sentence: "To prevent brute-force attacks on the password, the maximum allowed number of negative password verification attempts can be set using AUTHLIM. This mechanism is disabled by setting AUTHLIM to a value of 000b, which is also the initial state of NTAG21x." So Philips went out of their way to secure that toothbrush head. That's reassuring.
- HarHarVeryFunny 3y agoMaybe time to boycott Philips for their woke enforcing of 3-month toothbrush replacement, and closed-source toothbrushes! (just kidding)
- james-redwood 3y agoNext up: 2FA for your toothbrush
- qingcharles 3y agoWelcome Time Travellers! This is 2023 where you can find yourself locked out of your toothbrush after too many failed password attempts.
- BLKNSLVR 3y ago"Unauthorised Bread" https://arstechnica.com/gaming/2020/01/unauthorized-bread-a-near-future-tale-of-refugees-and-sinister-iot-appliances/ https://arstechnica.com/gaming/2020/01/unauthorized-bread-a-...
- parpfish 3y agoI hope that this is a warning to time travelers from the past and not a friendly welcome to time travelers from the future that are looking back on simpler times.
- jamesdwilson 3y agoKind of concerning this could turn into another toner ink situation
- babo 3y agoIt works happily with a brush head without NFC. That was the first thing I tried with my new toothbrush.
- brianleb 3y agoIt works /right now/. Revisit this comment in 3-5 years and see if the behavior of new brushes and brush heads has changed for the worse...
- catchnear4321 3y agolocking down heads will hurt what market share philips still has far more than it hurts their consumers. there are alternatives, and even a locked brush is an alternative - it still works, and actively pisses off the user. people skip brushing their teeth for all sorts of reasons. (yes you do. stop lying. your dentist doesn’t believe you, either.) people go out of their way to not skip coffee.
- SV_BubbleTime 3y agoIt can’t be far off that they ship a BLE or Wifi enabled Sonicare that reports your best brushing habits to the app that then posts it on Facebook for philipPoints you compete with your friends on… oh shit… what have I done!? Anyhow, blocking unofficial heads is just an OTA firmware update away.
- nl 3y agoUmm this has been a thing for ages. Although the points don't go to Facebook - you get "rewards" for them. Eg: > Pair one or more brushes to our iOS or Android app, then you’re all set. quip’s Bluetooth® Smart Motor will automatically store your routine, no phone needed! To check your brushing stats and the points you’ve earned, tap the app. > Earn bonuses for never missing a beat! Redeem points for rewards you’ll love https://www.getquip.com/store/products/smart-electric-toothbrush-set https://www.getquip.com/store/products/smart-electric-toothb...
- AlbertCory 3y agoI have one, but it never occurred to me to want to hack it. "But how do you know when it's time to change the brush?" Well, how about when it starts getting soft?
- mikestew 3y agoHow about when the blue part goes away, as documented? :-) I've used a Sonicare for, what, ten years or more? And I don't think I've ever seen an indication that the NFC is communicating anything to me. That's not to say that it isn't, but if I'm going to ignore something[0] and replace the head when I damned well please, I just ignore the blue part of the bristles. I could probably adjust my behavior to ignore whatever flashing LED the NFC sets off, but after so many years I'm just going to continue ignoring what I always have. [0] I'm either easy on toothbrush heads, or Philips is lying, because when the indicator says "buy a new head" it still has plenty of life IMO. Bristles straight and tall, just like a new one, but no blue left being the only difference between that and new. So I ignore it and get a new one when the bristles go a little wonky.
- jrockway 3y agoI just change the brush head on the 1st of every month. They say it lasts for 3 months, I must press too hard. So it goes.
- mikestew 3y ago...I must press too hard Could be. My wife presses so hard, I hear the motor bog down. "JFC, honey, let up a bit", to no avail. She's constantly replacing her heads. I literally can't remember the last time I popped a new one on mine. I could easily believe it's been six months (and, yeah, it's about due).
- PlunderBunny 3y agoThat’s probably really bad for your wife’s teeth.
- josephcsible 3y ago> that the tag is configured to permanently disable all write access after three wrong password attempts Why is this kind of thing legal? For how many politicians and activist groups claim to care about the environment, why hasn't anyone introduced a bill to ban intentionally turning useful equipment into waste? Any legitimate security needs would be fulfilled just as well by doing a full wipe and factory reset instead.
- mikestew 3y agoWhy is this kind of thing legal? For starters, my experience says that, unlike an HP printer, your toothbrush still works just fine[0] if you ignore anything that tells you to replace the head. [0] At least as fine as a toothbrush with a worn-out head is going to work.
- josephcsible 3y agoI don't really mean about the toothbrush. I mean, why is it legal for NXP to make chips that permanently brick instead of just factory resetting when too many wrong passwords are tried?
- JohnFen 3y agoWhy should it not be legal to make such chips?
- josephcsible 3y agoBecause they take control away from the actual owners of devices, and they, unnecessarily contribute to e-waste, for no increase in real security.
- JohnFen 3y ago> they take control away from the actual owners of devices Only if they're used that way. They don't take control away from the actual owners of the devices if its the owners who put them in there, for instance. Again, I think you're conflating the existence of a mechanism with the abuse of the mechanism. If you were just railing against the abusive uses, I'd be behind you 100%. I just don't see why we should outlaw a common and useful mechanism entirely, rather than outlaw certain uses of that mechanism.
- deleted 3y ago[deleted]
- neilv 3y agoNow that the industrial design and manufacturing are figured out, Philips could do a number of additional things with NFC. (Especially with network access, possibly through an app, and more securely with a different NXP chip.)
- deleted 3y ago[deleted]
- hoosieree 3y agoI'd like to skip the whole "smart" toothbrush phase and go straight to the "smart ass" toothbrush, which razzes me about my sugar intake and gossips with the toaster behind my back.
- dumpsterdiver 3y agoAs a bachelor who lives alone, it would actually be very motivating if I overheard my appliances making hushed comments about how I "look a little more plump than usual."
- willi59549879 3y agoonly if it is true, but for that they would also need cameras on you at all times.
- jayd16 3y agoJust a scale on your smart toilet seat would do.
- wrycoder 3y agoHm, maybe I'll apply to YC. Except my version also has a sniffer and can detect C. difficile and SARS-CoV-2.
- DiscourseFan 3y agoDo you think I could get a smart fleshlight that measures my sperm-count and the average number of thrusts it takes me to finish?
- pajko 3y agoYou can skip the toothbrush part: https://www.lurahealth.com/ https://www.lurahealth.com/
- rddydydyd 3y agodumbest waste of materials. for what? just to waste more battery when i travel with it without a charger?
- tgsovlerkhgsel 3y agoFor reminding you to buy a new head. Complaining about RFID wasting battery in a mechanical device is either misinformed or intentionally reaching for bogus arguments.
- eternityforest 3y agoWe need a law like EUs USB-C law, except forbidding non-Qi wireless charging unless you have a significant technical advantage over Qi. Then we'd always have a charger.
- Tepix 3y agoI'm surprised this is the only comment that critizies the fact that now the brush head contains not just plastic but also a microchip. That can't be good for recycling. Not to mention the wasted resources during production of the chip.
- Dead_Lemon 3y agoI'm still trying to figure out why people need a battery powered toothbrush over a conventional one, let alone one that needs apps and verifiable replacement heads.
- arbitrage 3y agoPeople don't. A company wanted a new market, so they made one and convinced enough people that they do in fact want this superior brushing technology. Ooooh, so shiny.
- TheCaptain4815 3y agoI’ll never forget when my damn sonicare toothbrush app warned me about my iPhone being jailbroken. Had to have been a troll by the creators of the app since not even some of my banking apps had that warning.
- amlozano 3y agoAs a security professional, I often get asked whether adding a root check is advisable. My general recommendation is to go ahead and implement it, but with a focus on data collection rather than taking action. For instance, you can log if a user is using a jailbroken or rooted device, without interfering with their experience. The responsibility for running a secure operating system lies with the users themselves, not the application. Applications that attempt to restrict how users utilize the app can be likened to malware. Now, there might be instances where a business executive argues in favor of DRM or ensuring that certain coupons are limited to specific regions. In such cases, its sometimes suggested as a requirement to verify if the app is running in a simulated environment or is rooted. However, I can assure you that if you lock some kind of value behind this check and then rely solely on the operating system to provide this level of security, there will eventually be clever hackers who find ways to bypass the protection. The same principle applies to business-to-business apps that demand extensive control. In such situations, you need to rely on other software solutions or provide dedicated hardware. It's important to refrain from attempting to take ownership of my device, considering it's already under the control of Apple or Google anyway... /sarc. If you require stronger guarantees, I suggest reaching out to them.
- Zeyka 3y agoWhen I rooted my android phone a few years back, all of my banking apps worked (I had to use magisk hide for some I think) but the only app that would not work was the Macdonalds app... Not that I needed it, I never go there, but I thought it was funny that their app was more "secure" than some banking apps.
- Eavolution 3y agoI can tell you from a few weeks ago that Santander definitely does care and magisk hide does nothing for it
- aaronbrethorst 3y agoMe, dumb: I change my Sonicare toothbrush head whenever it tells me to. I haven’t had a cavity in 8 years. You, a clever toothbrush-hacking genius: haha, the head is new again! This is neat, and I find the process of reverse engineering the Sonicare toothbrush fascinating, especially sniffing the NFC communication, but please change your toothbrush head every three months.
- imp0cat 3y agoYes, I realize I might be in the minority here, but isn't this actually great use of a smart device? Not having to keep track of brush head changes, awesome! One less thing to worry about, as the device is smart enough to tell me when it's time for a new one.
- JohnFen 3y ago> isn't this actually great use of a smart device? You don't need anything to tell you when it's time to change your toothbrush. You can tell by feeling it, or in the extreme, by just looking at it. There's no need to track anything.
- rekoil 3y agoI've pondered it myself, for me it comes down to whether the company has implemented it in an ethical way or simply as a way to maximise profits. In this case I feel like they aren't being malicious, but I've only used the brush with compatible brushheads for about half a year (was using up my old ones from an older model first).
- m463 3y agoI got mine to buzz, but it never prevented me from brushing my teeth.
- charles_f 3y agoI kind hoped the conclusion would be that you could unlock hidden features in the brush head, increase the torque and reset the head so that you don't have to replace it. But alternatively, since the head has an NFC tag, could you use it for stuff like a partnership with Marriott (open your hotel door with your toothbrush, so much convenience) or with transit companies to charge your monthly transit pass? Possibilities of an NFC-enabled toothbrush head are infinite. The future truly is fascinating.
- mrfumier 3y agoThe toothbrush doesn't force you to change the head. You can brush your teeth with an old head as much as you want.
- charles_f 3y agoYeah but if you could reset the head instead of having to change it, imagine the savings
- eternityforest 3y agoI really don't think that permabrick after N incorrect attempts should ever have been considered as a sane feature. That allows denial of service extremely easily. What needs security just enough that it can't just be unencrypted, but also can't afford real security (like long passwords or public keys)? Does this have any use aside from DRM products?
- teekert 3y agoTFA does not suggest the head is bricked, the internal counter just stops updating. TFA does not even specify what the handle does in that situation. Supposedly it just keeps working with no issues.
- userbinator 3y agoI guess this is one of the downsides of ubiquitous cheap electronics --- DRM everywhere. A similar thing happened relatively recently with label printers: https://news.ycombinator.com/item?id=30420918 https://news.ycombinator.com/item?id=30420918 (...and people have come up with a "modchip" to bypass that restriction already: https://www.eevblog.com/forum/reviews/dymo-550-thermal-printer-drm-hacking/ https://www.eevblog.com/forum/reviews/dymo-550-thermal-print... ) All my tries to guess to one-way function for generating the passwords failed. In case anyone else wants to try having a go at this (without inspecting the firmware): ignoring the first and last two bytes of the UID, we see that 79 is farther from EC and D7 in a similar way that FF is far from 61 and 67, and EC and D7 look closer together too. I wonder if they used "real" crypto or just a simple XOR/shift/add/sub cipher. There's more info about the device itself here: https://device.report/philips-oral-healthcare/hx68 https://device.report/philips-oral-healthcare/hx68 (Unfortunately they've requested the schematics/block diagram/functional description to be kept "permanently"[1] confidential, and the inside photos are difficult for me to make out the part numbers on the MCU and other components.) [1] I wish those who have been leaking secrets about our government would've gone after stuff like this instead of things like the NSA...
- justsomehnguy 3y agoThanks for the news on DYMO, I missed it and I wanted to buy their printer...
- RobotToaster 3y agoIf anyone happens to be looking for an open source alternative label maker https://github.com/andreisperid/E-TKT https://github.com/andreisperid/E-TKT
- deleted 3y ago[deleted]
- joshspankit 3y agoI agree with another commenter who said enjoyable read. I’m normally all about hacks and whatnot, but I found myself much more drawn to the idea of scanning the toothbrush head after brushing to be able to automatically track brush time. No password required.
- fencepost 3y agoDoes the brush stop working with the head when that lockout happens, or does this just break the "buy a refill please" functionality? For my older Sonicare (with a larger brush head base), I've found it easiest to just write "Q1," "Q2," etc. with a sharpie when I replace the head.
- gempir 3y agoI own a Sonicare. All it does is vibrate and blink shortly after you are done brushing when it's time to "refill" It doesn't even do that after every time you used the head "too much". Not sure how much it reminds you.
- bilekas 3y agoThis is crazy interesting but I didn't quite understand, when the timer runs out the head doesn't work anymore or you just get an LED notification to get a new one, to me at least there's a big difference in the two!
- teekert 3y agoI'm also curious!
- Shank 3y agoDepending on the model, it usually blinks an LED and vibrates a pattern to let you know it's time for replacement. It's definitely not a hard lockout or anything. The brush heads for advanced models also tell the brush which cycle to use and which intensity to vibrate at (e.g., for tongue cleaning brushes vs normal brushes).
- politelemon 3y agoBit meta, wanted to say this is one of the interesting posts on HN in a while. Good work on the author's part, following their curiosity, writing it up in an understandable way for the rest of us. They weren't successful in the end but still got far.
- expertentipp 3y agoThe innovation no one needs neither asked for, but the only one we get.
- CatWChainsaw 3y agoThe planet is burning and we deserve it.
- Raqbit 3y agoA few years ago I reverse engineered my Oral-B (Braun) toothbrush in order to change the color of the brush (handle) to one of my liking, without being constrained by the pre-set colors available in smartphone app. (Which I think now also requires you to log in) Turned it into a Go library: https://github.com/raqbit/goralb https://github.com/raqbit/goralb
- herrherrmann 3y ago“Goral-B” – Well done.
- GoToRO 3y agoSome facts: The tag is used to change the cleaning mode of the toothbrush automatically, to match the type of head you inserted. This makes very easy to change heads durring the same session. It is also used to register how long you used that head. A warning is shown when the head should be replaced. After a few warnings you will no longer get them, just the led to replace the head remains on. You can continue to brush your teeth without any problems. What I've found is that the warning comes at the right time, you really feel a decrease in cleaning efficiency around that time. You can use heads without the cip and they work. You just have to select the proper mode from the handle manually. Or not. The early versions have a defect where when you push to insert the head, you also push to open the handle. With time, water will get in and the toothbrush will stop working. Not sure about the latest versions.
- bagels 3y agoIs it less effective because they slow the motors down or other trickery?
- oehpr 3y agoThis is a good question, but people are pretty sensitive to pitch changes, I think we would detect the motor slowing down. It would be super easy to reveal as well. A family member with the same toothbrush, your head finishes first. Motor slows down, pitch goes down. Compare the two. Replace the old head, now they're the same. Scummy practice revealed. Scandal. That said. I'm not totally sure on the mechanism that all electric toothbrushes use. It's much harder to detect subtle amplitude changes.
- GoToRO 3y agoThe bristles wear out. Their heads wear out but they also become soft from all the vibration so they dont't push as hard on the teeth. Also gunk might accumulate depending on how careful you rinse it. Still better than a manual brush even in that state.
- NwtnsMthd 3y agoNo, it doesn't appear so. It seems the bristles do wear out somehow, to me it appears that they simply become less stiff over time. The change to a new brush head is noticeable. This should be relatively easy to verify. One could take a new brush head and forward its counter to the limit, directly comparing it to a new unmodified brush.
- nologic01 3y agoFitting a GPU inside a toothbrush feels like the ultimate existential risk.
- WeylandYutani 3y agoI love my oral b io (as I should it's a 200 euro toothbrush) but never understood why it needs to have a Bluetooth chip.
- als0 3y agoWhy did you pay €200 for a toothbrush?
- uxcolumbo 3y agoIt's a toothbrush. Why does it need all this tech and an app? It's better to think about sustainability. I had an Oral B IO electric toothbrush. The retail price is nuts and the brushes are expensive and can't really be recycled. Imagine millions of these out there slowly rotting. I gave up on the IO and bought this one instead. Simple design and battery lasts longer too. https://www.trysuri.com/ https://www.trysuri.com/
- sp0ck 3y agoAnalogue/manual toothbrush is like 1-2 Euro. Product You are promoting is 85Euro. Assuming my normal toothbrush lasts 3 months for 85 Euro I have backup for 21 YEARS. Spare ones are for ~5.6 EUR piece. I will stay with using my hand ;-)
- uxcolumbo 3y agoElectric toothbrushes are more efficient at removing plaque and help to avoid gum disease. If your immune system doesn't react so aggressively to plaque then yes manual tooth brushes are cheaper and you have many sustainable options in this space, i.e. toothbrushes with a wood handle etc.
- Arch-TK 3y agoNot having fillings is worth a lot more than spending £96 every 5 years (electric toothbrush £40 + £2.80 head every 3 months).
- m_mueller 3y ago> I will stay with using my hand have to use your hands?? that's like a baby's toy!
- chillbill 3y agoWhy do you need an electric tooth brush to begin with? Just get one of those old Jordan ones you can probably get one for as low as $2.
- marcod 3y agoI mean, you can find disposable electric toothbrushes in stores ... sustainability does not seem to be among the primary design criteria.
- chrisstu 3y agoGood article from an intellectual curiosity perspective. I use the Philips Sonicare brushes, although I've been using 3rd party heads for years due to the cost difference (3X cheaper). Philips obviously wants to deter people like me from this behaviour. I see they no longer sell non-RFID heads, even when the old brushes lack this feature. Yet more e-waste as they try to nudge customer upgrades.
- Aardwolf 3y ago"The smart handle and smart brush head pair is a powerful combination that enables Smart replacement reminders" Is there any consumer to whom this would read as a positive sales pitch?
- zomg 3y agoi've been using sonicare toothbrushes for 10+ years and the only difference i have noticed with the "smart" version is horrific battery life. amazing innovation! :\
- ubermonkey 3y agoAll I know is that I absolutely never, ever, ever want my toothbrush to be "smart." We need to stop putting firmware in things that don't need firmware. Not everything needs a chip or intelligence. The rampant abuse of this kind of thing leads to shitty products and an uptick in electronic waste.
- fsflover 3y agoThe chips are not a problem. Nonfree software is.
- JohnFen 3y agoI disagree. For a toothbrush, the chips are a problem. If nothing else, manufacturing chips is very bad for the environment. We shouldn't be putting them in things that don't need them.
- fsflover 3y agoIf we were talking about the climate problem, you would be right. But your comment is a goal shifting, because I replied to the problem of abuse of the firmware in the chips. Abuse can't happen with free software.
- ubermonkey 3y agoLOL
- ubermonkey 3y agoNah. Putting firmware in shit that doesn't need firmware is itself a problem, even if it's free.
- fsflover 3y agoI don't see a problem really. What's wrong with being able to fine tune, e.g., how strong the vibration is? Maybe my teeth are more sensitive than usual. Or between 'sensitive' and 'normal'.
- dxld 3y agoHacking the NFC comms is fun and all, but it turns out you can just rip out the orange flatflex PCB under that metal ring with a screwdriver and the brush doesn't care :) Stops it from beeping at you when your allotted product lifetime is up though.
- gwbas1c 3y agoI just want to point out that resetting the timer is a really, really, bad idea. My toothbrush heads are usually very worn when my toothbrush tells me to change the head. (And I honestly suspect I should change them before the toothbrush tells me to.) Anyone remember the old hole punches that would let you turn cheaper, low-density floppies into high-density floppies? A lot of those floppies ended up having data loss.