No more wasted trips to the mailbox! The Wireless Mail Alert System consists of a wireless sensor and a plug-in receiver that work together to notify you when your mailbox has been opened. Simply affix the sensor to your mailbox lid with the included adhesive tape and place the receiver inside your home (up to 350 ft. away). When the mailbox is opened, the receiver beeps 4 times and a red LED illuminates to let you know your mail has been delivered. Works on all curbside, wall-mounted and slot mailboxes.