The Gatekeeper is a self-contained, tackle box-size unit that eliminates the need for a gate. Equipped with a motion-detecting "eye" that triggers an alarm, it hangs on one gate post with the eye facing the other gate post. When the eye senses movement, the alarm is activated, emitting ultrasonic, doublemodulated sound pulses that frighten the animals away and train them to avoid the gate. The unit is powered by a solar panel or an internal 12-volt rechargeable battery. (A charge lasts about two months.)