Of course, there are about 3 types of variometers:-
The ancient one, which consists of (IIRC) 2 fluid-filled tubes, one with a red floating level indicator and one with a green floating level indicator. As you hit rising / sinking air masses, either the green or the red float rises up the tube, according to whether you're in lift / sink.
The 2nd type is more or less a VSI (with the same construction and working on the same principle) but with a much more sensistive indication of lift / sink. This is purely mechanical.
The 3rd type (which is what cwatters refers to) is electronic and has a variable audio tone according to the rate of lift / sink. This is particularly useful when trying to centre on patchy thermals as you can stay 'heads up' rather than trying to scan your vario whilst trying to dodge all the other pilots who are trying to get in on 'your' thermal
It's a very quick reacting instrument and can be really irritating during normal flight or when well established in a thermal. It does have its uses and IMHO is a good flight safety feature for gliders.