A detection system invented by a university graduate may provide a simple way of preventing dementia patients from getting lost.
The system - dubbed a high-sensitivity field interference wander detector, comprises a sensor fixed to the door and a metal needle worn by the user.
It rings if a user goes out of the door.
David Cheung Wai-sun, 48, a master's graduate of the School of Creative Media at City University, did not disclose the principles behind the system, for which he is applying for a patent.
But he said his invention did not rely on airwaves, which are used by similar products.
The sensor, which is made of several circuit boards, costs about HK$7,000, while the 2cm needles cost only HK$8 each.'It is less than half the price of similar products that are on the market,' Mr Cheung added.
He said, for example, that if a nursing home bought detector watches that cost HK$300 each for 100 residents it would cost a lot more.