Automatic trailer backup alarm activates 97 dB repeating pound pulse to alert bystanders and other drivers in areas such as congested dock operations and near walkways where vehicle is moving in reverse. Wheel-end direction sensor reads ABS tone ring activating alarm after one-half of reverse revolution of tire. Alarm ceases 2 sec after trailer stops or immediately upon forward movement. System requires no communication with tractor and has reverse polarity protection and reset fuses. Kit includes direction sensor, electronic control, wiring harness, and alarm.