Don Jenkins wrote:

My garage door opens by itself from time to time. The make is called
"Challenger", and it is distributed by Swift Garage Door Systems.

Can anyone suggest a cure?

As Christian has said, you can try changing the control codes. However,
if you are unlucky enough to have quite high radiation levels around
you( Neon lights, Phone (or police) transmitters, radio amateurs?), you
may never totally get rid of the problem and could settle for key
operation. I experienced a similar problem on a secure control system,
with a 43 digit code. Random noise gave the correct coding sequence
about once every 20 minutes.

Regards
Capitol