A or fenceless boundary is an electronic system designed to keep a pet or other domestic animal within a set of predefined boundaries without the use of a physical barrier. A mild electronic shock is delivered by an electronic collar if its warning sound is ignored. The system was first invented and patented by Richard Peck in 1973 and was held until 1990 by Invisible Fence Co, now known as Invisible Fence Inc.

In some pet fence systems, there is a wire (which may be buried) that emits a radio signal to activate the receiver collar. Other pet fences are wireless. Rather than using an underground wire, they emit a radio signal from a central unit, and activate when the pet travels beyond a certain radius from the unit.