Abstract: A theft prevention system for use with business machines having a housing, including a base and a removable cover includes an alarm, which is connected to a microswitch having a spring biased plunger that projects downwardly, through an aperture formed in the base of the housing, and abuts the surface upon which the machine rests. The microswitch is positioned such that when the machine is lifted from the resting surface, the plunger is biased into an active position thereby actuating the alarm. A protective sleeve which is fixedly connected to the resting surface surrounds the plunger and extends upwardly into the housing through the associated aperture thereby inhibiting tampering with the microswitch. A second microswitch may be provided which includes a spring biased member that is disposed in abutting relationship with the cover of the housing and functions to actuate the alarm when an attempt is made to separate the cover from the base.