No, the gas board tried to sell them to us @ £38 each while he was servicing our central heating, he told me "we can only fit them while we are at your house doing some other job"!!!!! basicaly he was saying if you don't buy them now tough or was that before you get chance to find out how much cheaper they are on the high street and install them youself?
You can buy a cheap twin pack from asda that will tell you if you have a problem but wont be a long term solution, were gonna buy a couple of ones that look like smoke detectors, and get your gas appliences serviced regularly.
Calvin & Anne