FireAngel smoke alarm stupid engineering

[Cerebus]

No you're not the only one although I suspect very few people bother. I test mine properly as well. I take some plastic wrap off some bread, stick it on a fork and set fire to it.

Enough about your cooking skills. He asked you how you test the fire alarm. 

[MrMobodies]

I see from the picture a test/reset button and their table below:

https://cdn2.hubspot.net/hubfs/2274469/FireAngel/Manuals/WST-630%20Manual.pdf

Page 9
WST-630 LED Indicators

Red Led:
Flashes once continuously every 45 secs     
Normal Operation

Red Led:
Flashes once every 45 seconds
Single chirp at the same time as the red LED flash
Fault
Call Technical Support if within warranty. If not replace alarm immediately

A red led that flashes to say it works and and doesn't work when it is with a chirp.

When there is a fault or it is tampered with (removed from the ceiling or a breakage in the mechanism when it is put back) I would want it to go off and there to be a dedicated LED that is clearly marked in the plastic as fault for faults. Would that increase costs but they did get in there another amber led, a radio communication module and the decorations.

If the fault causes it go off constantly and the battery is sealed in there that can become a nuisance.

Page 12
MAINTENANCE
WARNING: This device contains a powerful lithium battery. If tampered with, the battery may be shorted and create a fire hazard. Never attempt to open or damage the battery .

Sounds scare mongering to me and the way it is written sounds a bit silly advising not to open it for one wanting to damage the battery.

[tom66]

If you open the device you will probably damage the precise optical sensor, flexing the board to remove the board from the plastic or when desoldering the battery.  If you want removable batteries buy a device designed for that.  It is a life safety device.  One thing I would never repair is a smoke alarm unless I could thoroughly test it. And that really requires a calibrated test tunnel.

If you have removable batteries you need a tag that sticks out to warn the users that the batteries are removed.  And reverse polarity protection.  This is a requirement in EN14604.  It adds a fair bit of expense to the product, both in assembly and parts. 

The FireAngel devices are £10 smoke detectors. That means they're coming out of the factory in China for £3-4 each.  If you want a really good smoke detector buy a Nest detector. Removable batteries, clever sensor design, substantial self diagnostics, wifi connectivity.  It's a good device.   But it's a £100 device because you're paying for some decent hardware.

No one want to listen to the guy who actually designs these for a living? These decisions aren't made on the basis of things being there to frustrate engineers, they are designed to be cheap. It is better to have smoke detectors that not installed in a building. Even if they aren't perfect.

[bd139]

I know that a singular market focused opinion is a data point and not something we can base a conclusion on thus I can't solely take your points onboard. I know as a contractor, looking in from the outside has a lower degree of assumptions than looking out from the inside.

I disagree on a couple of your points.

Firstly, I can't possibly agree that anything with the complexity of a Nest device is a good thing. The thing is an IoT device that actually presents multiple attack surfaces and doesn't necessarily have sound functionality. I cite this as my source:

https://www.cpsc.gov/Recalls/2014/Nest-Labs-Recalls-to-Repair-Nest-Protect-Smoke-CO-Alarms/

The failings are:

1. Nest Wave was turned on.
2. This disabled the smoke alarm if there was any activity near it.
3. It had to be cloud connected and pull a software update to disable the feature.

Alas the last issue due to the sheer number of unaccounted for devices, ended up in a full recall of 440,000 devices. This "seemed like a good idea at the time" is how most of the IoT market operates. The inevitable reply I'm going to see which I will mention here was "that was an old version" and "it doesn't work like that now". That's not an excuse for fucking it up to start with.

And then there's the problem of what happens if your smoke alarm is silently bricked or broken by an update? Google, Nest's parent company, hosed 25 handsets we had via automatic updates. And what happens when Google eventually decide to can it. It's no longer smart. It's an attack surface and a risk. IoT devices are already posing a significant risk to security.

Secondly, price does not necessarily reflect fit for purpose. A £3 device may be considerably better than a £100 device. That's what your aforementioned EN 14604 standard is about. Both the £3 and the £100 device should pass functional testing to conform to that standard.

What is important for smoke detection really based on my trite evaluation?

Well the risk appears to be defined by two classes:

1. It didn't go off.
2. It packed in.

Thus evaluating that into characteristics to operate smoke alarms:

1. Diversity. One class of device from one vendor is clearly untrustworthy. That is obvious by the sensor disparity between optical and ionisation sensors and the functionality that is provided. Deploy multiple optical and ionisation detectors from different vendors (I have 2 of each in my house for ref now).
2. Regular testing. Weekly basic "is the device still working". Quarterly "does this thing actually still detect smoke". This builds a failure model for the devices and pre-empts failures.
3. The MTBF appears to be pretty shit despite advertisements otherwise. Replace it every year. That pre-empts failures. This is cost effective.

That's slightly more sound engineering thinking than throwing all your eggs in one IoT basket.

[tom66]

Yes, I'm deliberately avoiding talking about IoT because I don't use any IoT devices (attack vectors being one reason, but not the only reason.) My evaluation of the Nest device is based on it as a standalone device; and it is perfectly possible to never connect the Nest devices to the internet.  You can create an interlinked network without Wi-Fi and the devices will sound without Wi-Fi too. They use Zigbee for in-home communication.

The early Nest sensors were badly designed and prone to false alarms.  The GenII device is far better with a dual blue/infrared smoke sensor. It is similar to an industrial EN54 type fire alarm and has a low false alarm rate but sounds alarms early.  Sure, no excuse.  But that's the Silicon Valley approach - move fast, break things.  I don't necessarily agree with it.  But I am saying the GenII Nest is a well designed, high quality device; I have never looked into GenI as they stopped selling that pretty quickly.  I know one of the consultants who worked on the design of GenII with them, and I know the company who sold them the calibration and test kit. They know what they are doing.  I have a badly abused Nest device on my desk.  It complains it can't find its microphone or LED light ring and chirps about this.  But it still works fine.  Detects smoke at 0.03dB/m.  Impressive.

When it comes down to EN14604 there is little spec in the way of long term product life. If you build a battery into a device, it has to last 3 years minimum. If the battery is replaceable, it has to last 1 year minimum.  And when the battery is low the alarm has to be able to sound for 4 minutes before dying;  and the low battery fault chirps have to be able to go for at least 30 days before dying.   There is no requirement to detect sensor fault conditions, such as an open circuit LED or implausible zero offset.

In terms of sensitivity there, too, is no actual specification. This might sound a bit mad but the basis is the device has to pass on test fires (TF2-TF5;  ranging from a petrol fire, to insulating foam, to wooden sticks heated by an electric heater, and one other I can't remember right now.)  If it passes these then the sensitivity is adequate (but there is about an 8:1 range of acceptable sensitivity.) The key requirement is that the sensitivity remain stable (+/-60%) after applying some "abuse" to the device, like impact, high temperature, low temperature,  battery low,  humidity,  corrosive atmosphere etc.  Also, the devices you make have to be within a roughly 2:1 window for sensitivity,  including the supplied test samples.

I think that the lack of a specification for sensitivity is a mistake in EN14604  but it is how the standard is written. In theory manufacturers can release high sensitivity and low sensitivity alarms if required. And there are some alarms on the market that adjust their sensitivity with temperature in the room, in an attempt to detect real fires quicker.

Your approach to diversity is probably reasonable, but at the rate at which you go through devices you might begin to consider a central fire alarm system, or more expensive, well designed devices like the Nest GenII.  Also, a test with the aerosol cans, which are available for around £10 each, would be a good idea, once every quarter.

[MrMobodies]

The FireAngel devices are £10 smoke detectors. That means they're coming out of the factory in China for £3-4 each.  If you want a really good smoke detector buy a Nest detector. Removable batteries, clever sensor design, substantial self diagnostics, wifi connectivity.  It's a good device.   But it's a £100 device because you're paying for some decent hardware.

No one want to listen to the guy who actually designs these for a living? These decisions aren't made on the basis of things being there to frustrate engineers, they are designed to be cheap. It is better to have smoke detectors that not installed in a building. Even if they aren't perfect.

I think I'd be looking at a commercial fire alarm. I have seen  install smoke detectors connected up to burglar alarm systems back many years ago but I was told that regulations now require them to have their own control system and fire resistant braided kind of cables.

[Mr. Scram]

If you open the device you will probably damage the precise optical sensor, flexing the board to remove the board from the plastic or when desoldering the battery.  If you want removable batteries buy a device designed for that.  It is a life safety device.  One thing I would never repair is a smoke alarm unless I could thoroughly test it. And that really requires a calibrated test tunnel.

If you have removable batteries you need a tag that sticks out to warn the users that the batteries are removed.  And reverse polarity protection.  This is a requirement in EN14604.  It adds a fair bit of expense to the product, both in assembly and parts. 

The FireAngel devices are £10 smoke detectors. That means they're coming out of the factory in China for £3-4 each.  If you want a really good smoke detector buy a Nest detector. Removable batteries, clever sensor design, substantial self diagnostics, wifi connectivity.  It's a good device.   But it's a £100 device because you're paying for some decent hardware.

No one want to listen to the guy who actually designs these for a living? These decisions aren't made on the basis of things being there to frustrate engineers, they are designed to be cheap. It is better to have smoke detectors that not installed in a building. Even if they aren't perfect.

Using Nest is asking for trouble. I have to agree with bd139's assessment here. Treating detectors as disposable makes a fair amount of sense.

[Iwanushka]

I test my smoke detectors this way.
1. Does it react to vape crap from 1m
2. Does it react if I exhale cigarette smoke 0.5m away
3. Spray can...

Edit crap detectors that we have with fire alarm system at the office trigger only if you chain smoke cigar from 5cm away... and that's lots of smoke...., basically they react when half of the room is full of smoke, and according to all standards and fire dept its okay, its only okay if you set it this way in a damn smoking room e.g. hotel where you can smoke but then again that thing is 5-10m away smoking from the sensor and no chain smoking cigar or pipe will still trigger that crap