The name confuses people, because a motion metal detector has nothing to do with burglar alarms or sensor lights. It describes how the machine reads the ground. Motion machines ignore anything that stays constant and report only what changes as the coil passes over it, which is exactly what lets them work in mineralised British soil without screaming at you.
New to the hobby? Start with the beginner range. Working beaches? See the beach detecting page, where salt handling matters more than anything else.
One that only produces a target signal while the search coil is moving. The circuitry looks for changes rather than absolute readings, which lets it ignore the mineral content of the soil and report just the target. Nearly all modern hobby detectors are motion machines.
Because that is how a motion detector works. It reports change, and a stationary coil over a stationary coin produces no change. Sweep back over the target and it sounds again. Nothing is broken.
For nearly all detecting, yes. Motion machines cover ground faster and give you target identification before you dig. Machines that hold a stationary signal are better at judging the depth and size of one deep target, which is a much narrower job.
Around one metre per second, which feels unhurried. Keep the coil flat and within an inch or two of the ground through the whole sweep, and overlap each pass. Most missed targets are missed because the coil lifted at the end of the swing.
Yes, provided the machine has proper salt handling. Wet salt sand reads as a constant signal, and a motion detector with a beach or salt mode tunes it out. Without that mode the machine will chatter badly on wet sand.
It can give you a strong hint. Target ID numbers and tone breaks separate iron from non ferrous reliably, and with practice you learn the signatures of ring pulls and bottle tops. It is never certain, which is why everyone digs more rubbish than treasure.
Not to start with. Buy a good motion machine, learn it properly, and only add a specialist depth machine if you move into cache hunting or deep single targets. Several C.Scope models give you a pinpoint mode anyway.
The Lander XD50 at £79.95 if you are testing whether you enjoy the hobby, or the Reflex G6 at £249.99 if you already know you are staying. Both are motion machines and both handle ordinary British soil without fuss.