A hand held instrument for carrying out some function on a
work piece. The instrument is a handpiece that is held by the
user and includes a working element at the distal end of the
handpiece for working on the work piece. There is a source
of power that activates the working element by providing
power thereto in various forms. There is also a pressure
sensor that senses the pressure between the working element
and the handpiece. In one embodiment that pressure sensor
senses a predetermined pressure in order to couple the power
source to the working element for activating the working
element. In another embodiment, the pressure sensor senses
a reduction in pressure between the working element and the
handpiece to illuminate an indicator light.