How do the electronic pet doors sense that my pet is approaching?

The electronic pet doors we carry use a magnet as the collar key, or use a battery powered infra red collar key. The magnet type creates a very small amount of electricity inside the pet door when it nears the outer frame piece. The door senses the electrical charge, and reacts with an electric solenoid which pulls the lock down, allowing the door to be pushed open. The other type of electronic pet door we carry uses an infra red collar key. These electronic pet doors work in much the same way as the remote control for your TV, and are also very reliable. There are other types of cat and doggy doors on the market which use radio frequency keys, but we have found the magnetic and infra red key types to be more reliable. ... more