How does magnetic strip lap timing work at racetracks - automotive?

Answer 1

For In Car / Kart Timing:

Located on the bottom of the car / Kart is a hall effect switch (similar to a reed switch but solid state, more sensitive and quicker to switch). This switch detects the magnetic strip which is fitted into the race track as the car / kart drives over it. This triggers the lap timer on the steering wheel and displays your lap time.

For Circuit Timing:

Each car / kart is fitted with an active RFID chip (transponder) which is constantly sending out its unique code over radio for a distance of about 1m. As the car / kart drives over the timing loop, the loop reads the unique code and tells the main timing system to trigger for that car / kart. In most profesional races the position of the transponder is regulated to ensure no advantage is gained by mounting it as far forward as possible. Some motorsports i.e. F1 demand more than 1 transponder in case of failure.