Definition: kill switch
Hardware or software that immediately stops an operation. Stemming from the big red button often found on dangerous machinery that is pressed in an emergency, a "virtual kill switch" is a function in software that shuts down the device. For example, in smartphones, a kill switch can be activated remotely if the device is stolen in order to prevent someone from obtaining sensitive information.
In order to deter criminals from stealing smartphones, in 2014, California enacted a law requiring all smartphones sold in the state to have a remote-controlled kill switch by July 2015 that would render the device useless.