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Is it really ultrasound? Microphones on phones may be able to pick this but what speakers are able to play even 20 kHz? And these apps should always listen, th
by ungzd 9y ago
Is it really ultrasound? Microphones on phones may be able to pick this but what speakers are able to play even 20 kHz?
And these apps should always listen, that will drain battery quickly, so these apps will be listed in top power-consuming apps and user will notice it.
- Cyph0n 9y ago18-19 kHz is usually high enough; smartphone speakers can play that fine from my experience. Yes, battery drain is an issue. Most apps use a background service that wakes up at a fixed interval. The longer the interval, the longer the broadcast has to be though, so it's basically a trial and error kind of thing.
- MichaelMoser123 9y agoAnother issue (besides the privacy issue) is that it may be annoying for pets. Dogs and cats can hear these sounds. Also the apps on the phone have access to the microphone (even though they probably do not need this permission for any other purpose), so these apps are all potential listening devices.
- williamtrask 9y agoi'm so glad you said this... made my day
- zdkl 9y agoClock sync? Protocol usually is to check NTP and broadcast at prechosen times if you wanna keep the battery drain down.
- Cyph0n 9y agoI'm talking about the phone receiving a broadcast. The app has to be designed efficiently such that it minimizes network activity and doesn't hog the input audio stream. You also have the issue of trying to maximize the probability that a device in proximity to a beacon will pick up the full message. So you need some redundancy, which obviously increases overhead. NTP sounds like it would work. As you kindly noted, just make sure the beacons broadcast at a agreed upon time and in fixed increments.
- mercurysmessage 9y agoI wouldn't be so sure about users knowing, unless they are told. Plenty of users use apps that drain a lot of battery.
- posterboy 9y agoyour first point coupled with diminishing free air range in bands above 40kHz makes this hack seem like a futile attempt to simply gather as much data as possible, as low or uncorrelated as it might be. Some phones might be more cappable than others, however, and air is dense enough for several meters of significant ultrasound transmission at low power. With e.g. Samsung TVs always listening, I wouldn't be surprised if they optimized the speakers and micros in that regards, while benign applications aren't out of the question either. The second point however is an overly broad generalisation disregarding the technical inaptitude of the target group of such apps (wherein I might include myself).
- URSpider94 9y agoI don't think people are using true ultrasound, e.g. 40kHz. In most cases, it's more like "poor man's ultrasound" at 19 kHz, Just outside the hearing range of most people. They have to stay as close as possible to the human hearing range to avoid audio low-pass filters and simple capability envelope of the speakers and microphones.
- chippy 9y agoThe article gives the example of speakers in physical stores, so I imagine they would be special ones that could transmit ultrasound. Additionally, the article states that phones are mainly just the receivers.