Abstract: A vibration sensitive switch has a pair of spaced apart parallel contacts (4) housed in a switch body (1,2,3) and a movably supported activated mass (5) inside a chamber (6) in the body. The mass (5) is supported by conductive members in the form of a pair of bars (14, 16) secured in the mass and located between the two contacts (4) with the center of gravity (Cg) of the mass (5) spaced from the points of contact between the contacts (4) and the bars so that bars are urged against the contacts (4) by a lever action as a result of the gravitational force acting on the mass (5). The forces at the contact points are thus greater than that which would be obtained by simply allowing the mass to rest on the contacts, which enables a relatively small mass to be used having a greater sensitivity to high frequency vibrations.