Let me save you the time and expense of testing UL2034 approved CO dectectors.
If you go to: http://www.gastechnology.org/webroot...rts/020112.pdf
you can read the Gas Research Institute report on "The Performance and Reliability" of UL approved home alarms.
Some of their findings were:
- 38% of alarms purchased in retail outlets didn't work, brand new, right out of the box
- UL requires that the test button only test the buzzer, not actually the sensor.
- models with digital displays were so inaccurate that they "seeming displayed random numbers"
UL strictly prohibits an alarm from ever, ever, alarming below 70 ppm......
Most UL approved alarms are also cross sensitive to a bunch of common household cleaning products, paint, high/low humidity and, due to the lousy (cheap) sensor technology, are guaranteed to alarm when they reach the end of the sensor's life....
If you want a 'professional grade' alarm (that really works) you need to get one from CO-Experts or NCI - all the rest are ..... junk.....