THEY HAVE been marketed as useful for gaining the upper hand at poker, receiving covert advice during tricky business meetings and helping with surveillance.
One was alleged to have been secreted on George Bush's person during a presidential election debate.
Now anxious students have been revealed as another potential market for firms keen to sell that staple of subterfuge: the hidden earpiece.
The Government's testing regulator is concerned that students may be using the devices, possibly linked to mobile phones or iPods, to cheat in exams.
An unnamed teacher has passed information to the Qualifications and Curriculum Authority about a company that is openly promoting the "completely invisible, completely wireless, exclusive micro spy earphone" to desperate exam candidates worldwide.
A spokeswoman for the authority said: "As a regulator, we take this, and any other cases of malpractice, very seriously and are looking into it."
On its website, the aptly named "Examear", based in Toronto, Canada, boasts of its ability to help students succeed, claiming that their product "greatly fits the needs of students who are doing a test, exam or any class-based assignment".
Its earpiece is available in three versions. The silver model, costing $185 (pound;86), is "especially designed for high schools". It has a hidden earphone that connects to a mobile phone while the student uses a microphone to communicate, presumably by whispering to a friend. It has a four-hour battery life, which the company says "should be enough to complete any complicated and tedious testexam".
A gold model, at pound;100, could easily hook up to an MP3 player, says the firm, allowing students to pre-record their notes for use in an exam.
At pound;140, a platinum version features Bluetooth technology, allowing the user to connect to a mobile phone without wires.
The website indicates that the company has had British customers.
Other firms provide similar services. A France-based company, GSM Earpiece.com, offers a "spy earpiece" at pound;110 for use with a mobile phone. Users simply wait for a friend outside the exam hall to tell them the answer.
Its website offers the following quote purporting to be from an American student: "I partied all night long and still passed my history exam with flying colors. It's amazing!"
In April, schools in the US were reported to be cracking down on the use of iPods, on to which students could pre-record answers that allow them to cheat in tests.
American students have claimed it is possible to get away with running the wire up their sleeve to an earpiece and listening to it while leaning on a hand.
In Britain, cheating of this level of sophistication is less well-known.
Students are banned from taking mobile phones into the exam hall and can lose marks if they are found to be carrying one, even if it is switched off.
In 2005, The TES reported that some 1,013 pupils had been penalised for mobile phone-related offences.
The QCA spokeswoman said that the information about Examear would be passed to the Joint Council for Qualifications, an umbrella body for exam boards in England, Wales and Northern Ireland, which defines test malpractice.
Examear did not respond to a request for comment this week.
CHEATING IN EXAMS
* The age-old techniques of copying from a neighbour or looking over the shoulder of the person in front are still in use.
* Getting someone else to do the exam for you has led some schools to insist on photo IDs and to calls for fingerprinting.
* Mobile phones can be used to access material or communicate with others.
* Students have bought leaked exam papers on the internet for up to pound;400, though many turned out to be fake.