Inventor devises a sound idea

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.

The detection system has been in use in six nursing homes for several months and another four are in talks with Mr Cheung.

'The needles are small and not driven by electricity, so it is less likely dementia patients will detect their existence and take them off,' said the inventor.

He also suggested that the system could be applied in hospitals for the mentally ill and in pet shops for animals.

Mr Cheung was inspired to design a detection system after reading a news report about an elderly dementia patient who left home and got lost.

'At that time, I was taking a business course and the teacher asked each student to think of an idea for a profitable business,' Mr Cheung said.

'I thought it would be wonderful if I could invent something useful for those patients and run a business on it at the same time.'

He had previously designed a webpage editing system and a clotheshorse that can indicate whether clothes are dry.