Tripping Up Intruders with Tripwire

A plastic ring has a circumferential groove formed in its outer peripheral surface. The ring is fitted in a bowl-type centrifuge rotor such that the ring's outer surface contacts the inner wall of the rotor. The channel is defined by the groove and rotor wall. The rotor is filled with a compensating liquid to reduce centrifugal stress on the plastic and to reduce leakage from the channel.