WHEN I was 13 my best Saturday entertainment focused on making prank phone calls and knocking on people’s doors before running away. Nothing beat hiding in the hedge with my best friend, crying with laughter as Mr and Mrs Miserable stalked furiously up and down the street looking for the perpetrators of these crimes against their weekend peace.

Once you have left school that kind of mucking about is not well tolerated. But I do miss these jokes. There is nothing better than witnessing self-engineered confusion, so I was interested to hear about the latest juvenile prankster phenomenon known as bluejacking.

For the uninitiated, bluejacking is the art of sending anonymous — and free — mobile phone messages via Bluetooth-enabled devices to other Bluetooth phones within a range of about ten metres. Using a phone with Bluetooth, you can easily create a new phonebook contact and write whatever message you want in the “name” field. Then you can ask your phone to seek other Bluetooth devices (mobile phone, laptop or PDA) within your wireless range and send that contact to them. A message with whatever you have written will pop up on their screen — and most victims will have no idea where the message comes from. This is where the fun starts. Personalised messages such as “Nice yellow shoes!” can have the most startling effect on the unsuspecting passer-by.

The idea of bluejacking originated in the online discussion forums of the Esato website that is a favourite with Sony Ericsson phone-owners. Phone geeks have been doing it for a while, but it looks likely to become a common joke — if not a global phenomenon. Matthew Towers, a senior Bluetooth analyst with IMS Research, said that for the first time total Bluetooth product shipment worldwide has exceeded one million units a week and that, after a shaky start, short-range wireless technology is making its way into a record number of consumer products. Despite this he can’t see the joke taking off. Towers concedes that the publicity cannot hurt Bluetooth — the reverse, in fact — but says that “there is only so much fun you can have sending anonymous messages”.

Ellie, 13, from Surrey, disagrees. She is a regular bluejacker who has set up the first bluejack-dedicated website that tells the curious exactly how it works and how to achieve the best results. I was curious, so thought it only right that I accompany her on a research expedition.

Ellie goes to school, so a weekend was the only viable option, and would also provide a shopping crowd, as bluejacking is fun only if there are lots of potential victims. It is also easier to escape detection in a crowd.

I arrive feeling sceptical about the amount of fun to be had hanging out with a 13-year-old — even such a cool one — in shopping centres. The first thing Ellie says is: “By the way — this easily beats knocking on doors and running away. The expression on their faces is totally priceless.”

Right. Like, whatever dude. My (borrowed) phone goes down very well, however, and we head for Starbucks after a quick briefing.

It is important to go bluejacking where people will be wandering around slowly. You will find it difficult to locate other Bluetooths if people are moving too fast for you to keep covert and within range.

Ellie’s favourite haunts include shopping centres, coffee shops, train stations, shopper-filled high streets, cinemas, restaurants, bars and mobile phone shops. Starbucks did not yield the victims we had anticipated, although it provided good practice time before hitting a big Boots. We loitered near the hair dye and found the place awash with Bluetooth units. Strangely, a lot of people seem to name their phones. Out of a possible five, Ellie chose Magdalena.

Ellie usually sends: “You have just been bluejacked.” The possibilities, however, are endless. We scout the area listening for the telltale message beep. Result. A tall, spiky-haired guy across the aisle reaches into his pocket and whips out a snazzy-looking phone. He reads the message with a bemused look on his face and shows it to his girlfriend. She is more interested in the shampoo and tells him to shut up.

I egg Ellie on to send another one — “Like the spiky-hair, Magdalena” — and we lower our heads as we feign fascination with John Frieda. His phone bleeps again and he reads the message, an expression of growing astonishment on his face. He tells his girlfriend to stop it, convinced that she is playing a trick on him. She reads the message and assures him that it wasn’t her. This is brilliant.

I can’t resist one more. They move over to a “buy two, get one free” section, and Ellie — inspired — sends him “3 for 2”. At this point the guy looks decidedly scared, head swivelling in all directions — a bit Michael Douglas in The Game, and although I am desperate to fool him some more I don’t feel inclined to explain to Ellie’s father why his daughter has been arrested. She is after all wearing one of the jumpers she sells on her website — a hooded sweatshirt emblazoned with the words BluejackQ.com — but, in his terror, Magdalena has not noticed.