I originally had a simple garage door opener which just had a switch setup for a code. When the remote failed I updated to the newer type with much more complex digital coding. This is supposed to be very secure but if you have your garage full of stuff, and you leave the control in the car outside, all a robber has to do is to break a window on the car to get into the garage and probably the house.
This time the receiver failed, and I decided to make a remote with a keypad so as to thwart this vulnerability.
This is therefore two devices, a transmitter and a receiver. This is a photo of the receiver which was made to be compatible with the power provided by the door opener and its control wire.
The reason why it uses a D-9 connector is to be compatible with a programming cable. It is easily removed to take to a computer to reprogram for a code change.