said by an inspector :
... how long can one gaurantee that home to remain leak free?
If there was any hint of a leak to call in the inspector - for example even the faintest smell - you should really monitor for methane leaks from now on.
You can buy commercial units but for someone with a bit of electronics experience/interest, it is a simple DIY project. Replace the sensor every year. »www.sparkfun.com/products/9404