A lavalier microphone is a small microphone that can be clipped onto a person's shirt to record his or her voice. Usually dynamic or electret microphones, these lapel mics usually have their own power source in the form of a small battery pack with one AA battery. The small size of lavalier microphones make them ideal for sit-down interviews as they provide a close perspective sound and block out a lot of ambient sound, such as traffic and wind. Many lavalier microphones are omni-directional, which means that the direction it is pointing is not significant. This also means that it can pick up other voices or sounds from nearby, however, which can distort the speaker's voice.
Lavalier microphones are used for a wide variety of productions, ranging from stage plays to film sets, and are relatively inexpensive to purchase. They can be wired or wireless, depending on production needs, and are good for scenes that don't involve a great deal of movement. If the person wearing the microphone is going to be moving significantly, his or her clothing is likely to rub against the microphone and cause static. It is, therefore, a good idea for someone to test the setup before use. An assistant can wear headphones linked to the microphone to help detect if the lavalier microphone begins rubbing against the wearer's clothing.
Also, the person wearing the microphone is relatively limited as to how they can turn their head, so as to avoid any distortions in sound. If used for film, it's a good idea to use lavaliers in conjunction with a boom microphone, to make sure that all relevant sounds are recorded properly. The unwanted sounds can then be edited during post production to achieve the desired result.
If a lavalier microphone is expected to be used for a prolonged period of time, it is a good idea to have a few extra batteries on hand. Some good old-fashioned duct tape can also help to keep it anchored in the right position.