Police are investigating how a small camera came to be concealed within a smoke detector in a male toilet at the Belmont Forum shopping centre.

The discovery was made by an electrician on Friday. He told Channel Nine news that he noticed a smoke detector flashing. When he opened it, he discovered a small, cordless camera.

The hidden camera concealed in the toilet smoke detector - as featured on Nine News.

The worker, who didn't want to be named, reportedly said it made him feel shocked, disgusted and sick.

The device was handed into centre management, which then called police.