I had the privilege of watching a grey haired, experinced electrician work. The task of the moment was replacing some electrical sockets at the church. He had a "doctor bag" of all kinds of fun items. He walked up to one socket that needed to be replaced. Out of his bag of tricks, he pulled a rig that was a junction box, with a neon bulb and a big push button. This connected to about a foot of wire, and a three bladed plug.
He put the plug into the socket, and the neon bulb lit up. He took hold of the juncion box, and pushed the button. I heard a circuit breaker go "KLUNK" down the hall, and the neon bulb went off. I realized at that moment what happened, he had shorted out the breakerr and now the socket was safe to work on. Seriously kewl!
He counsells me that the push button needs to be at least 75 amp rated, or the contacts will burn off. I built such a device with a 15 amp switch and neon bulb combination. That didn't make it through one use, the contacts fused. My next model was a good two dollar 20 amp toggle switch, but I lost the neon bulb indicator. No loss, I just plug in my three bulb tester in the other socket. I labelled the switch plate "off" and "pop". I had it out for use, and a kid who was watching asked "What's off and pop?" which is now the name of the device.
This technique is not reccomended in buildings with Federal Pacific Electric panels. I assume no responsibility for people who build their own gadgets. I'm sure others have described the Jesus Method, using a short length of insulated wire. I won't describe it further. Less safe than Off And Pop.