At the airport, when you put your bag on the conveyor belt and walk through the metal detector,you're probably thinking more about your flight than your brief, high-tech journey through the security gate.

What happens as you and your bag pass through?

When you walk through the arch of the metal detector, pulses of electromagnetic energy pass from one side of the detector to the other. These pulses travel fairly easily through the body, but metal can speed up, slow down, or even change the shape of the energy wave. When the receiver on the other side detects this kind of change, the machine beeps.

How much electromagnetic energy passes through your body? For comparison, an electric can opener emits about four times more than an airport metal detector. According to Bryan Allman of EG&G Astrophysics, a company which makes security detectors, no studies have shown any harmful effects of electromagnetic energy from airport metal detectors, and they don't interfere with pacemakers.

The bag you place on the conveyer belt goes on a different kind of journey, through x-ray beams. X-rays are also a form of electromagnetic energy, but they have a much, much higher frequency than the pulses emitted by the metal detector. The amount of radiation an airport x-ray scanner gives off is relatively small, about 40 times less than a medical x-ray. Still, exposure to enough radiation over time can damage living cells. That's why you shouldn't hop onto the conveyer belt, but the x-ray won't harm the contents of your bag; it won't even cloud the film in your camera.