How it works:
1. In the beginning the door is locked, cat is outside
2. Cat walks up to the gate, RF tag gets read within about 4 inches
3. Door unlocks and a light comes on.
4. Timer ensures that door stays unlocked long enough to give cat a chance to respond
5. Cat pushes open the flap and enters
6. Flap falls back, activates Hall effect sensor, and the door locks
7. Going from the inside out, an infrared proximity sensor detects the presence of an animal if within about 10 inches and unlocks the door.