Carbon monoxide sensor

The older ones had a piece of cardboard with some chemical coating that darkened as it absorbed CO. They used an LED and a photodiode to sense the darkening. It would gradually darken from PPBs of CO or some other stuff in the air.

I think the new ones are also electrochemical and eventually get poisoned. Mine seem to last about 5 years, so I guess we have pretty good air.

The issue becomes, what do you do when the alarm goes off?

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I have one in my camper van which emits an ear-shattering "Beep-beep_beep!!". Normally I would open a door or window when the diesel stove is running but on one occasion I was trying to be very stealth in an upper-class neighbourhood where I had spent the night and probably hasdn''t cracked open the door far enough, for fear of being noticed.

I was making a cup of tea early in the morning when suddenly the alarm went off, so I had no option but to immediately depressurise the stove and open the big sliding side door for ventilation. The noise of the alarm was enough to wake the whole neighbourhood and the button I thought would silence it had no effect. Trying to cover the sounder grille with one hand, I took the alarm off the bulkhead and shook out the batteries.

I'm sure this isn't the procedure recommended by the manufacturers.

But if you take the batteries out and go back to bed, will you die?

I guess if you have two and only one makes noise, it's probably OK.

In California, all smoke detectors include CO sensing and have 10-year lithium batteries, so we have several CO detectors in the house.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

Not with the side door of the van wide open and the stove stopped.

After a few minutes I put the batteries back in, replaced the alarm on the bulkhead and re-lit the stove - this time with the back door propped open a couple of inches. In really bad weather I have found that putting on the cab heater blower gives adequate airflow with all the doors and windows shut.

I suspect the cause of the problem was the flame of the alcohol I use to pre-heat the main burner, impinging on the cold parts of the stove. When it is running properly, the heat from the main burner generates large enough convection currents out of the vent holes to draw in sufficient fresh air.

One reason they start loud is to ensure it wakes people up from a deep possibly CO induced sleep. I tested ours by wafting some smoke at it.

Very loud and it took a while to calm down (removed batteries till it did). CO poisoning from those small gas fired hotwater heaters used to be all too common - a few tourists are killed that way every year.

Most annoying thing is on cold winter nights when the battery terminal voltage gets low they will emit a very short 120dB peep every few minutes that is impossible to locate reliably so you have to go around and stand under each one waiting for it to do it again.

They are cheap and cheerful consumer products (even the expensive ones).

ISTR that in the Three Mile Island disaster they spent the first fifteen minutes of the emergency trying to silence all the different damn alarms that made it impossible to think in the control room. Only once they had the noise under control could they communicate with each other across the room. It was part of a human factors course on best practice interface design with good and bad examples.

Aircraft have got much more sensible warning and alert systems making the simplifying assumption that the pilots don't want to die.

One in our village hall went rogue last week. I needed my apple picking tool to remove it from the ceiling. It was so loud that I didn't want to get any nearer to it! It had a sounder disable switch on the back.

Again battery fail in the cold weather but instead of an annoying bleep it went off as if there was a fire. Luckily the neighbour is deaf!

I worked in a university where they had just one sounder for each floor, mounted at the end of a each corridor. They had made it loud enough to be heard in the laboratories with all the doors shut. It would have been safer to climb out of a window than enter the corridor and try to escape past the sounder.

When it went off one day, nobody could find out what was happening because communication was impossible.

Our main lab which was very new at the time had magnetically held open fire doors at intervals all along the main corridors. When there was a real fire or a fire alarm test they would close almost in sequence end to end. One of my friends was an unintended casualty hit from behind by a big heavy fire door whilst watching the one in front of him close.

Think the opening sequence corridor of "Get Smart" from the 1960's. Our fire doors were like the first set he meets.

Are you sure about that? 200dB is a couple of atmospheres. This would probably be enough to demolish your house.

You may want to think that over. 200dB is like a rocket launch, close up. 300dB would be 10^10 times more powerful.

Jeroen Belleman

Correction: 1 pico watt

Correction: Using the correct reference level of 1pW means it would only be 1 billion nuclear power stations.

How can companies compete fairly when their claims are so obviously made up? Why should I believe one impossible claim is better or worse than another impossible claim? John

It is the marketing and sales guys that are to blame. Their job is to sell the product and get their sales bonus.

Lead time on our kit (~ 4 yr build time) was such that they would have no hesitation in offering a product that would require the repeal of one or more laws of physics. They would invariably have moved on before the product was actually delivered.

Salesmen take their sales bonuses and run. It is up to scientists and engineers to somehow deliver on what they have promised the customer.

Impossible claims that are beyond known laws of physics are worse.

Impossible claims that are difficult engineering but if made to work would open entirely new frontiers are actually rather fun to work on. If a bit of a white knuckle ride...

That's not just a strawman, that's a whole army of them!

Obviously you're embarrased over this 300dB remark.

You should be.

Jeroen Belleman