notbob wrote:
On 2011-10-30, mike wrote:

I'd be interested to learn how you determined that it did not "properly
work"?

the readout never changed. put in oven, hold in car exhaust, reset,
whatever.... always read "30".

nb
Well....
If you put it in a KNOWN CO-free environment for a day and it still
reads 30 after reset, take it back, it's busted. Even a crappy
CO detector should read zero when in a Zero CO environment.
A couple of dead lcd segments can turn that zero into a 3.

Everything I've seen on testing detectors says, "Don't test 'em on car
exhaust."
The OTHER stuff in car exhaust contaminates the element.

If your oven put out enough CO to register, you'd be dead.
40 years ago, we used open flame gas space heaters with zero
ventilation.

For most detectors, the sensor or the electronics attempts
to emulate the human response. It takes a while to register.
Shorter for higher concentration.

Detectors vary considerably in the coarseness of their readout.
3-digits does not necessarily get you 1ppm resolution.
I'd expect the readout to be conservative.
False alarms cost the vendor money/reputation. Dead users, not so much.

To answer your question,
I have a low-level sensing unit by COexperts www.coexperts.com

There's lots of info there.

According to them, they do not comply with UL requirements
because the requirements are unsafe. They use an electrochemical
sensor with real-time display plus a logging function. They claim
1ppm resolution and alarm at 7ppm.
Mine's never detected anything.

List price is $250. Have no idea the street price. Mine came for free
with an energy audit.