  We present simple arguments that detectors moving with constant acceleration
(even acceleration for a finite time) should detect particles. The effect is
seen to be universal. Moreover, detectors undergoing linear acceleration and
uniform, circular motion both detect particles for the same physical reason. We
show that if one uses a circularly orbiting electron in a constant external
magnetic field as the Unruh--DeWitt detector, then the Unruh effect physically
coincides with the experimentally verified Sokolov--Ternov effect.
