Home Depot offers the General Tools Pen Style Natural Gas Detector for $29.31. (Amazon charges the same.) Opt for in-store pickup to avoid the $5.99 shipping charge. That's the lowest price we could find by $7, although it was $3 less in June. It detects LNG, LPG, CH4, methane, and butane gas and features a natural diffusion sensor and audible and visual alarms.