The boys, pupils at St Thomas of Canterbury College in Christchurch, developed the cheap device as part of a business competition for school pupils.

They have also had interest, and orders, from schools and universities in New Zealand. A mobile detector lets you know when phones are being used surreptitiously and can cost hundreds of pounds. The gadget was deemed to be the best product in the local sector of the Young Enterprise competition.

"It's grown outside the Young Enterprise thing," said Adam Manley, one of the 17-year-old managing directors of StopCom, the name the students have given to their company for the competition. The pupils have sold all 20 of the first models of the detector that they are building, and are developing their next generation product.

'Robust product'

The detector, which they have called CellTrac-r, works by picking up the bursts of radio frequency activity that emit from a mobile each time it sends or receives a call or a text message. The device can detect these bursts of electro-magnetic energy up to a radius of 30 metres. It can also measure the amount of the energy to determine the distance of the mobile.

The detector then lights up light-emitting diodes - when four LEDs are lit, a mobile is in use close by. Just one lit LED means that the phone is being used at a distance of 25 to 30 metres. Local company Tait Electronics has helped guide the students through the process of building a business.

The boys have also been able to call on a technical advisor from the electronics firm, helping ensure both a robust business model and a robust product. "At the technical level, it's [CellTrac-r] got good integrity," said the boys' mentor, Tait's intellectual property manager Frik de Beer.

"It's designed for mass manufacture if they have to get to that point.

"The product is not a toy. It's relatively simple. Because of that the cost is reasonably low."

Cheap as chips

The first version of the product has sold for just NZ$39.95 (£15), but if the boys develop an upgraded version, perhaps adding in a buzzer, and increasing the detection range, it would sell for around $100.00 (£35). The low price is probably part of the lure for would-be buyers as mobile phone detectors can sell for much more.

"We wonder why they sell it for so much," said Mr Manley.

"We've worked it out how much you should sell it for and these ones are selling for nearly $1,000 (£350). It's crazy."

Linda Roberts, who helps organise examinations at the University of Canterbury, plans to trial three of the detectors at this year's end of term exams.

"Some of these phones are very smart and very small. People could be texting away in an exam of 400 people and it would be hard to detect," she said.

"We've had an increasing number and [longer] duration of toilet visits in exams and with the technology these days, we have no way of knowing what's going on."

The local prison service is also planning to test one of the school boys' products.

"We are certainly having a look at it to assess its value for us," said Tony Coyle, national crime prevention coordinator for the public prison service.

"Prisons are difficult places because they are quite large and cellphones are very small."

Future plans

This year, these would-be entrepreneurs will not be reaping any riches as a portion of any profits from the boys' efforts will go to the charity that the school supports in Tanzania.

But the enterprising students may set up a private company once the school year and the competition ends.

"It is something we have thought about but we are not finalising it all yet," said Manley. First, there is the school to finish and exams to pass and a competition to win.

The results of Young Enterprise competition are due to be announced at the end of October.

Source: BBCNews