Spike Mike Law and Legal Definition

Spike mike is an electronic listening device consisting of a microphone attached to a foot-long spike, with an amplifier, a power pack, and earphones. [Silverman v. United States, 365 U.S. 505 (U.S. 1961)]

Spike mikes are used by police by inserting the spike through a wall separating an observation post from premises suspected of being used for criminal purposes, until the spike contacts a heating duct serving the suspect premises, so that conversations throughout the premises are audible to police officers listening with earphones.