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I'm wondering how much testing Nest did with the photoelectrics in the smoke detector. A teardown [1] seems to show a rather simple design for the led and photo

I'm wondering how much testing Nest did with the photoelectrics in the smoke detector. A teardown [1] seems to show a rather simple design for the led and photodiode beam path, as well as both of those components having places for light to potentially leak in around the diode bases. Other detectors [2], [3], seem to have much more complicated beam paths, with baffles and such, as well as better shielding to ensure the sensitive components are well-protected. Given this, I can see how all the differences in tolerances can lead to gaps which lead to lots of false alarms. [1] https://www.ifixit.com/Teardown/Nest+Protect+Teardown/20057 https://www.ifixit.com/Teardown/Nest+Protect+Teardown/20057 [2] http://www.accuratebuilding.com/images/publications/education/photoelectric_smoke_detector.png http://www.accuratebuilding.com/images/publications/educatio... [3] http://st-nso-us.resource.bosch.com/media/us_product_test/05_news_and_extras_1/product_news_1/06_productnews_fire_1/automatic_fire_detector_420_series_1/explodedview440.png http://st-nso-us.resource.bosch.com/media/us_product_test/05...

raldi 12y ago
> A teardown seems to show a rather simple design Don't you usually want lifesaving devices to have simple designs? For example, scuba breathing regulators are famously reliable in part because there's very little to them. Same goes for the AK-47, though I suppose I'm getting off the "lifesaving" track now...
- fencepost 12y ago
  I don't want lifesaving devices to have simple designs, I want them to have designs sufficient and appropriate for the task at hand. "Reduced manufacturing cost by $0.25/unit" in a triple-digit-cost smoke detector is not something that I as a consumer care about.
  - raldi 12y ago
    My point is that sometimes, simplicity isn't about reducing manufacutring costs; it's about creating a better product.
- Sanddancer 12y ago
  I'd argue overly simple. The nest, and the other detectors, both have baffles in them to block out light from the outside world. However, the Nest negates some of the benefits from this by having the LED shine against a piece of plastic at an angle fairly close to the photodetector. If that piece of plastic happens to be especially reflective, or if the photodiode and/or LED happen to be misaligned, it would be more likely to trigger false alarms. The baffles in the other detectors, on the other hand, are also used to ensure that the light from the LED gets nowhere near the photodiode unless light's being scattered by smoke. The Nest design works great in the lab, but when assembled en mass, hits a bunch of tolerance issues that leads to a more jittery product.
  - raldi 12y ago
    That's a reasonable possibility. I'm looking forward to seeing a teardown of the next release.
- Perdition 12y ago
  There is a difference between "being as simple as required to reliably function" and "being as simple as possible". False activations of things like alarms are dangerous because it conditions people to ignore the alarm or react slowly.
- agumonkey 12y ago
  I think he meant naive. We all want the simplest design possible that is correct, fault tolerant, etc etc.
- revelation 12y ago
  But it isn't simple? Look at that circuit board for gods sake, that's probably 6+ layers and apparently required custom gaskets around crucial components. If you consider the device as a whole, it is not simple at all. That's kind of the crucial point, too. A smoke alarm can only be considered simple when everything on the path from smoke detector to alarm is simple, and that's not the case here. Which makes this seem like a case of not getting the basics right.

raldi 12y ago

> A teardown seems to show a rather simple design Don't you usually want lifesaving devices to have simple designs? For example, scuba breathing regulators are famously reliable in part because there's very little to them. Same goes for the AK-47, though I suppose I'm getting off the "lifesaving" track now...

fencepost 12y ago
I don't want lifesaving devices to have simple designs, I want them to have designs sufficient and appropriate for the task at hand. "Reduced manufacturing cost by $0.25/unit" in a triple-digit-cost smoke detector is not something that I as a consumer care about.
- raldi 12y ago
  My point is that sometimes, simplicity isn't about reducing manufacutring costs; it's about creating a better product.
Sanddancer 12y ago
I'd argue overly simple. The nest, and the other detectors, both have baffles in them to block out light from the outside world. However, the Nest negates some of the benefits from this by having the LED shine against a piece of plastic at an angle fairly close to the photodetector. If that piece of plastic happens to be especially reflective, or if the photodiode and/or LED happen to be misaligned, it would be more likely to trigger false alarms. The baffles in the other detectors, on the other hand, are also used to ensure that the light from the LED gets nowhere near the photodiode unless light's being scattered by smoke. The Nest design works great in the lab, but when assembled en mass, hits a bunch of tolerance issues that leads to a more jittery product.
- raldi 12y ago
  That's a reasonable possibility. I'm looking forward to seeing a teardown of the next release.
Perdition 12y ago
There is a difference between "being as simple as required to reliably function" and "being as simple as possible". False activations of things like alarms are dangerous because it conditions people to ignore the alarm or react slowly.
agumonkey 12y ago
I think he meant naive. We all want the simplest design possible that is correct, fault tolerant, etc etc.
revelation 12y ago
But it isn't simple? Look at that circuit board for gods sake, that's probably 6+ layers and apparently required custom gaskets around crucial components. If you consider the device as a whole, it is not simple at all. That's kind of the crucial point, too. A smoke alarm can only be considered simple when everything on the path from smoke detector to alarm is simple, and that's not the case here. Which makes this seem like a case of not getting the basics right.