Virtually all new cars are supplied with a remote control to unlock the doors and turn off the alarm. This is very convenient, but not without its problems.
Some use infrared but most use a radio transmitter to send a coded signal to a receiver on the car.
The operating frequency (418Mhz or 433.92Mhz) is close to those used by MoD communication, radio amateurs and other common applications. Interference can occur and in the worst cases the car can’t be unlocked.
Modern cars are much less likely to suffer from radio interference but the problem remains for older cars, particularly those built before 1995.