Whilst they appear to be an innocent toy, and are advertised as such on eBay and Amazon Marketplace, they are serious devices to prisoners who smuggle them in to prisons across the UK to make illegal calls.
They are largely constructed of plastic, in order to evade metal detectors.
Possessing a mobile phone in jail is a criminal offence carrying a two-year sentence and an unlimited fine.
A prison service spokesman said it was already making efforts to detect the devices, reaffirming that "a range of techniques - including body orifice security scanners and high-sensitivity metal detectors - have seen the number of recorded seizures increase." More than 7,000 phones were confiscated in prisons in the UK last year.
Available for purchase from around £40 from popular online auction site eBay, and retailer Amazon, these can be easily concealed from prison guards allowing inmates to make and receive calls and texts.
A spokesman from Soca said the police unit had asked car manufacturers to take a stand on the issue – with the Society of Motor Manufacturers and Traders commenting: "We are aware of the existence of these mini-mobile phones and that a number of them bear resemblance to car keys bearing manufacturer logos."
Anti e-crime groups are asking online retailers to stop selling the fobs, and members of the public not to buy them, while e-crime units of UK police forces have issues guidance on the key fobs.
"There is a strong possibility that these products were not put through the stringent safety testing UK products go through, which means that there is a chance they are electrically unsafe meaning they could cause fires and injure consumers through electrocution" said the Met Police's PCeU Police Central e-crime Unit.
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