Kidde
A gas alarm is meant to warn you of a gas leak in a small enclosed space such as an RV cabin. If your RV uses propane appliances, many owners want a working alarm. If you carry no propane or other fuel appliances, it is optional.
RV and camper owners with propane appliances.
Kidde Carbon Monoxide + Explosive Gas, Natural Gas & Propane Alarm, Plug-in with 9V Battery Backup, Digital Display, 85 dB Alarm, LED Status Indicators, 3rd Edition (ASIN B0DT1MS1D1). Amazon's page has the current price, specs and reviews.
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Check current Amazon listing (ASIN B0DT1MS1D1).
Fine print: The Dude has not personally tested this product. The details on this page come from the Amazon listing and can change; check the listing for the current specs, price and availability.