Mail Reminder Notification Alert - Wireless Mail Alert System Works on basic type of mailbox with horizontal hinges. Works up to typically 200ft to 250ft away Instant alert with beep sound and flashing mail indicator Sensor unit is powered with 2 AAA batteries (not included) Receiver unit is powered with 6V DC adapter (included) When installing the transmitter please note that the arrow should be pointing at you when you open the mailbox lid. This device is only to be used on a typical mailbox as shown in the image, it will not work on a vertical hinge mailbox.