GFCI (ground fault circuit interrupters) are the rarely-recognized heroes of the electrical world. They can protect a person who is unlucky enough to end up between the AC line and ground, and, if working correctly, are a life-saving invention used in almost every home, commercial and industrial building out there.
Although GFCIs come with a built-in test feature, AC outlet testers are available that simulate a true fault condition; that is, it actually induces a ground leakage to verify that the GFCI circuit actually works. However, I was thinking that, if used maliciously, these tools can be used to disrupt power circuits that are protected via a remote GFCI breaker; for example, outdoor power outlets on a building which generally are wired 2 to 5 per breaker.
If the breaker trips, then someone will have to go to the breaker room and manually switch the circuit back on, which can definitely cause headaches for anyone who needed to use that circuit.
The effects of this aren’t that dire. One can’t take out a whole building’s power infrastructure this way and the worst that happens will be some downtime until maintenance comes out to restore power. Still, that doesn’t mean some prankster would do this just to have a laugh at anyone who needed to use that power outlet later.