Smarthome Select 74771 Wireless Mailbox Reminder and Mail Alert System Audible alert Visual alert Wireless communication up to 300 feet Easy installation - sensor comes with double-sided high temperature 3M adhesive strips. Sensor requires 2 AAA batteries (sold separately) Works on almost all standard mailboxes Power Requirements : Receiver - 6V DC Power Supply (included) ; Sensor - 2x AAA batteries (sold separately)