Surveillance cameras, alarm systems, doormen, multiple locks that require many keys, that one neighbor who is always always watching: all of these are fairly standard-issue security measures that any thief worth their weight in stolen electronics will likely anticipate and prepare for. The crutch knife, however, adds an element of deadly surprise that next to no one sees coming—until it's too late.

Allow me to explain: A band of real estate investors was touring an abandoned home in South Philadelphia on January 2nd, apparently appraising it for renovation. Ekrem Uysaler, of Real Estate Management Advisors LLC, had the presence of mind to turn on his phone camera, recording a strange finding the group made on the dilapidated staircase. (Which, by the way, was strewn with broken glass, an addition I can only assume someone intended as an extra layer of protection.) They later posted it to Facebook, for posterity.

As they approach the stairs, one of the team members spots a trip wire along one of the steps. "Dude, that'll fucking kill somebody, bro," one voice says as the camera pans up, revealing the jerry-rigged murder trap above.

"It's on a fucking crutch, a knife," another voice says. "This is homicide!"

Curious, of course, the guys grab a long piece of spare wood, jab the trip wire, and down comes the death contraption: A chef's knife duct-taped to a metal crutch, positioned to stab an unsuspecting interloper squarely between the eyes.

Uysaler told NBC Philadelphia that he's walked into a number of dangerous situations while inspecting the city's abandoned homes, but the crutch knife beats them all. "People kind of were in shock," he told the outlet. "We're gonna finish out the project, but we just stopped right there." Their initial surprise has since melted to amusement, he said, comparing the booby trap to "'Home Alone' ... Philly style."

"A lot of these houses you go in, they're all shells and vacant," Uysaler told NBC. "Especially with the gentrification in Philadelphia, with the housing market growing at a rapid pace, people wanna keep on investing, you're going to come across these things."

You will also come across these things in New York: a brief search of the Gothamist archives suggests that the crutch knife is an established entry in the booby trapper's handbook. In 2008, for example, a Long Island man set up at least one crutch knife to keep intruders out of his apartment. Upon his arrest, he reportedly asked investigators, "Did anyone get hurt with my knives?" When they answered no, he added a disappointed, "I wish they did."

While we cannot vouch for the crutch knife's efficacy, we urge you to keep in mind that it has only one apparent purpose and that is to maim, even to kill. Please do not badger your landlord to install one, and please do not undertake construction yourself. Thank you and good night. I'll be taking the elevator. Nothing to fear there.