Give me the beat boys and free my soul
I want to get lost in your rock and roll
and drift away.

When the band drifts away from song tempo, one of two things happen; the song slows down or speeds up.  Most noticeable is the rushing during choruses and lagging during verses. This tempo-drifting can be controlled in two ways.  The first is by having high-caliber musicians who know how to keep a beat based off a tempo-leading instrument such as the drums...or their tapping foot.  The second is by using technology in the way of a metronome.

A metronome is a device that produces a regulated aural, visual, or tactile pulse to establish a steady tempo in the performance of music. 

A metronome can be used by all members of a band or by the few, or the one.  [Pardon the Star Trek reference].  For example, all musicians might have the metronome's click playing in their in-ear monitors (IEMs).  Only the guitarists and the drummers might have it.  Or only the drummer might use it.

In a perfect world, all drummers keep perfect time.  This world isn't perfect, so I'll skip any further discussion on that matter. 

A metronome can be included in a sound system using a few different methods.

1.  A metronome can be controlled by one musician, usually the drummer, and the headphone jack on the metronome can be piped into the sound system like it was just another input device.  That metronome channel would then be off as far as the main speaker sound, but it would be going out to the in-ear monitor system such as Avioms or other monitor control system. 

2. A click track can be inserted into the monitoring system (Avioms, etc) by using DAW products like ProTools.

There are a variety of metronomes out there.  My worship team is looking at the Tama Rhythmwatch because of the features and the large knob for quickly and easily changing tempos.

Jumping back to the definition of a metronome, there are three possible tempo indicators; visual, aural, and feel.  In addition to hearing a click from the metronome, metronomes can have a flashing light that flashes to the set tempo. There are also a few metronomes that have a wired attachment that the user can clip to their body.  It vibrates or thumps to the tempo.  For the three mentioned, I've only heard of the aural being used during a service.  It's hard to stare at a flashing light through a song.  And something thumping on my body - that's just weird!

Let’s go back to the metronome and the click track usage.  The nice part of a metronome is the simplicity.  It can be mounted on a drum kit and the tempo can be controlled by the drummer.  As for the click track, that has to be controlled by the sound guy.

A final note on using metronomes and click tracks; don't output them through floor monitors.  While there is a possibility it could work and not be heard by the congregation, as soon as a song ends if the "click" is still present, EVERYONE will hear it.