Seju, the company that brought you the Safe Drive personal alcohol detector and the Kiss Me bad-breath detector, also sells the EZ Gas Check portable gas detector. It detects propane gas at levels as low as 1/10 of the Lower Explosive Limit (LEL) and natural gas at 1/5 of the LEL.
Operating for over 40 hours on two AA batteries, the stick-shaped EZ Gas Check uses a MEMS sensor to detect the presence of natural gas and propane. To ensure proper operation, every time you turn on the EZ Gas Check it runs a self-calibration cycle. Green, yellow, and red LEDs display all clear, gas present, or get the hell out and call the fire department respectively. The alarm will also sound if the yellow or red LEDs light, alerting you audibly to the presence of gas.
A little warning: I see nothing about the device being intrinsically safe, and I wonder how wise it is to look for leaks with an electronic tool that doesn’t carry that rating. Also I’m not familiar with the quality of their products, but Seju’s website reads like it’s been translated into English, rather than written in English.
Pricing starts at $12 with free shipping at Amazon if your order is over $25. Otherwise you’ll pay $18 to $30.