Three women on holiday in Portugal discovered a carefully hidden video camera in the bathroom that was set to capture them while they showered.

Rubee Woo took to Facebook to recount their horror find in an apartment rental in the Portuguese tourist hotspot of Porto, explaining that her friend noticed something off about a power outlet.

"We quickly packed our bags, handed the apartment keys to the police and left. By the time we reached the hotel, it was 5am," Ms Woo wrote.

It's part of a growing trend that experts say is made possible by a boom in the sale of household objects that appear perfectly normal but conceal recording devices.

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With a few clicks of a mouse, virtually anyone can purchase hi-tech devices that would've once been the stuff of spy films — an alarm clock, pen, car key fob or smoke detector that also conceal recording devices.

A number of Australian-based websites market and sell hidden camera items, which have plummeted in price as demand has grown in recent years, and experts warn the laws protecting innocent people from misuse and abuse are inconsistent and inadequate.

"Fifteen years ago, the technology that was available was expensive and a bit quirky and was mostly bought by law enforcement, private investigators and uber-geeks," Bruce Baer Arnold, an associate professor of law and justice at Canberra University, explains.

"But we're seeing the Kmart effect where availability has boomed and prices have fallen, so now anybody can get their hands on them."

On one local site, a child's night light, a pair of headphones, a computer mouse and a car cigarette lighter phone charger are some of the objects that conceal cameras.

Watches, picture frames, wall clocks, TV remotes, notebooks and music speakers with hidden video recorders installed are also available.

A bedside table alarm clock with invisible camera lens will set you back about $200, while a baseball cap with video recording capability is $168.

"We don't have any real standards or control mechanisms for the development and sale of these devices," University of Technology Sydney law professor Kristopher Wilson said.

"That's an issue for cyber security as well as privacy. There's a plethora of flow-on effects from this."