Maybe it has been demagnetised by your mobile phone — or perhaps a member of staff is trying to teach you a lesson.

A former hotel worker has revealed the secret ways hotel staff take their revenge on unsuspecting guests, The Sun reports.

In his tell-all memoir Heads in Beds: A Reckless Memoir of Hotels, Hustlers and So-Called Hospitality, Jacob Tomsky said there were many ways staff got back at rude guests without them realising.

Mr Tomsky, who worked in the industry for a decade, described the tricks he and his colleagues used to avoid getting into trouble with their bosses.

“If you’ve been having trouble accessing your room with your key card, it means you’ve p***ed off someone at the desk, and they’ll re-activate your key card when they see fit. It’s called ‘key-bombing’,” he told the UK’s Daily Express.

Bored, overworked and often under-appreciated staff had plenty of time to enact their revenge, which might include minibar raids and prank calls, Mr Tomsky said.

He said the wealthier the guests were, the more likely they were to be loud and wildly abusive, and celebrities were the worst of them all.

“A lot of people are watching Downton Abbey now and they think, ‘Oh, I’ve got servants, too!’,” he said.

“Especially the affluent, they treat people as they never would otherwise. Meanwhile, hardworking people — who might be getting screwed — won’t say anything.”

Here are six inventive ways hotel staff have wreaked revenge on rude guests.

KEY-BOMBING

Having trouble accessing your room with your key card? You’ve probably upset someone at the front desk. They love to watch with amusement when flustered guests return to get the key reactivated.

MINIBAR RAIDS

You’d better look over your bill closely. Annoyed hotel staff often wander in and steal from minibars, or deliberately miscalculate your charges. If you’ve used valet parking, your car isn’t safe either.

FOULED TOOTHBRUSH

You may want to be cautious of your toothbrush — it may have been “fouled”, Tomsky warned. We’ll leave that to your own imagination.

PRANK CALLS

Tomsky confessed to making a drunken midnight phone call to freak out one particularly mean guest.

“I informed him he was an a**hole and he should sleep like s**t,” Tomsky said.

And it did make him feel better. “But I got to the point where I built a wall up. I got an incredibly thick skin, and I really didn’t care,” he said.

ROOM KARMA

Cause a scene while checking in? You’ll probably be downgraded to a lousy room.

“You probably could have had a really nice suite and you’ll never know it,” Tomsky said. “I became the master of instant karma. And if I saw a Black AmEx [American Express card] — watch out.”

GROSS DRINKING GLASSES

All of your drinking glasses have been cleaned — not with soap and water — but furniture polish, as apparently it makes them sparkle.

This article originally appeared on The Sun and was reproduced with permission.