A BBQ lighter uses something called piezoelectricity to generate a nice spark that lights the grill. "Piezo," in Greek, means "pressure," and you find piezoelectric materials in a number of different places. For example, all of these products depend on the piezoelectric effect:
  • The push-button igniter in a gas BBQ grill or fireplace
  • Push-button cigarette lighters
  • Piezoelectric beepers (common in digital watches and anything electronic that goes "beep")
  • Piezoelectric tweeters in stereo speakers
  • Sound-generating arrays for sonar, fish finders and ultrasound devices
  • Crystal microphones
  • Phonograph needles
  • Quartz crystals used in most digital clocks and timers as the time base
Certain crystalline materials (like quartz, Rochelle salt and certain ceramics) have piezoelectric behavior. When you apply pressure to them, you get a charge separation within the crystal and a voltage across the crystal that is sometimes extremely high. For example, in a BBQ lighter, the popping noise you hear is a little spring-loaded hammer hitting a crystal and generating thousands of volts across the faces of the crystal. A voltage this high is identical to the voltage that drives a spark plug in a gasoline engine. The crystal's voltage can generate a nice spark that lights the gas in the grill.

In a crystal microphone, air pressure deforms the crystal enough to cause very small voltage changes in the crystal. These voltage changes are amplified and used to record or transmit sounds.

Piezoelectric materials also work the other way -- if you apply a voltage across the crystal, the crystal will change shape. The change is very slight in most cases, but it is enough to drive small speakers. For example, if you have a digital watch with a beeping alarm, the beeper is a little piezoelectric speaker.

Here are several interesting links: