Thieves take off in Mercedes using anti-lock device

Thieves have unlocked and stolen a Mercedes without even needing the keys, in what British police believe is the world's first "relay crime".

The footage, shot in West Midlands, shows two people standing outside the vehicle, both carrying relay boxes - devices are used to extend the transmitting signal of automatic keys.

With one of the pair standing near the house, and the other near the car door, they are able to pick up the key's signal from the owner inside.

Automatic keys unlock a vehicle once they get within a small radius of it.

"The car's systems are then tricked into thinking that the key is present and so it is unlocked," police said in the Facebook video post.

"The thieves then drive off, with the whole crime taking just one minute."

Two months on, the Mercedes has not been recovered.

Police recommend owners who use these keys purchase a steering lock so a thief cannot drive away.