Police in Essex are investigating the discovery of a "hidden camera" in the toilets of a Costa coffee shop in Chelmsford.
Staff at the Riverside branch were alerted by mother-of-three Stacey Shah, who had taken her four-year-old twin boys to use the toilet yesterday.
She said she "felt sick" and had "goosebumps" after spotting the device taped securely under the sink.
The device has been seized by detectives and will now be analysed.
Mrs Shah, from Braintree, supports a national campaign for improved cleanliness in public toilets and regularly sends it pictures of facilities that don't meet standards.
"I noticed under the sink was not cleaned so I took pictures," she said.
"I didn't think anything of it at first but then I felt uncomfortable - and realised it was a hidden camera."
The device, in the branch's sole unisex toilet, was securely attached with straps and had four small LED lights on the front.
Mrs Shah, who is deaf, said she covered the camera with tissue before alerting staff with a written note.
"I felt goosebumps, shocked, mixed emotions," she said.
"I helped the boys on the toilet - then me - I'm sure it recorded this. I felt sick."
A spokesman for Essex Police said: "We received reports that a member of staff found what they believed to be a camera in Costa Coffee toilets, in Riverside Retail Park, Chelmsford.
"We have seized the device and are now working to establish whether any offences have been committed."
Mrs Shah said: "To be honest I don't know what to say to the person who did this.
"You think you can get away with it and answer is no. It's so sick."
A spokesperson for Costa Coffee said it was "supporting the police with their investigations".