UL & Kitemarked {A British Quality Standard] CO ALARMS are sold in UK,
all have to be "CE" marked;{European Compliance with ceratin European
Elec Safety Standards known as CEN's}

UK Government arm have done extensive Research on CO Alarms long term
reliability, and until this
Govt Dept known as the HSE, are happy it won't get added to our
Building Codes alongside Smoke & Heat Alarms.

Some well known brands, also available in US, go out of spec after 1
year; they are measuring to the current British Standard BS7860.

SEE
http://www.hse.gov.uk/research/subje...icpremises.htm
Only 2 brands passed muster; Nighthawk{Kidde} and SF; latter only sold
in Europe I believe.

Tests were done by Research arm of main UK Gas Utility, Advantica,
under contract to HSE.