A lavalier microphone (also-known-as a clip-on microphone) is a really small microphone that can be clipped onto clothing and is often part of a wireless system. You can get complete wireless clip-on microphone systems that include a transmitter, receiver and microphone, but you can also get separate clip-on microphones, each designed for wireless transmitters or cabled systems.
Connecting a Lavalier Microphone to a Wireless System
Every microphone manufacturer produces transmitters with a brand-specific connection port for the wireless microphone. As such, it's essential to match a microphone with the right connection plug to the right system. Sennheiser transmitters, for example, always come fitted with a locking 3.5mm TRS mini-jack or LEMO socket, while Shure transmitters will have a TA4F port, and AKG transmitters will have a TA3F port. Couple up the right clip-on microphone and complete a full wireless clip-on microphone system.
Clip-On Microphones for iPhone or Android Phones
As long as you have a model fitted with a mini-jack port that supports TRRS plugs, you can even plug a clip-on microphone directly into a smartphone. If your phone doesn't have a standard analogue port (so, a standard headphone socket) then you'll need a clip-on microphone fitted with a digital plug. Older iPhone models will have a Lightning port, while newer models have a USB-C port and most Android phones have a USB-C port.
Recording Lavalier Microphones via XLR
While there's nothing stopping you from hooking a lavalier microphone up to a mixer or audio interface, you need to check that the plug and socket are compatible. Here it's much easier to just pick out a microphone that can be connected via a standard XLR microphone cable, otherwise you could use a special microphone adapter plug.
Cardioid & Omnidirectional Clip-On Microphones
Clip-on microphones can feature either a cardioid or omnidirectional polar pattern (which describes the range within which the microphone picks up sound). Cardioid microphones only pick up sound coming from the front, so they're perfect for noisier situations. Omnidirectional microphones pick up sound from all sides and tend to have a more natural sound. However they are more sensitive to contact and wind noise, so they're better for less noisy indoor environments like TV sets.
