RV Approved 9V Battery-Operated Smoke Alarm. Approved for use in recreational vehicles and meets the latest industry standards. Easy to install and maintain. 4.25" diameter. It features a hinged cover that allows for easy battery replacements while the tamper resistant locking pin helps prevent premature battery removal. Also features a test/silence button for efficient testing to ensure alarm is working properly and end-of-life warning lets you know when it's time to replace.