tripwire

/T R IH1 P W AY0 R/
noun
  1. 1

    A cord or wire arranged so that when snagged or pulled by an intruder, it will trigger a detector or trap or a device, such as a land mine.

  2. 2

    Any means of detecting intruders.

verb
  1. 1

    To set a tripwire mechanism in (a location).

Source: https://en.wiktionary.org/wiki/tripwire