This is the one I use, less expensive and very accurate:

http://www.amazon.com/UEI-CD100A-Leak-Detector-Combustible/dp/B000HHTY7Q

I've been using it even more for the occasional home appliance repair task.
Just today I replaced an oven valve in a friend's gas oven, after she
detected a faint gas smell. No way to use soapy water there, the gas was
leaking from the nozzle. A few years ago I used it to also diagnose multiple
loose connections on the same oven, where the local GE appliance 'repairman'
told her to buy a new stove because 'everything was leaking'.

Karl
www.westyventures.com