http://www.independentlifesolutions.co.uk/frequency-precision/chair-pressure-mat/

The chair leaving alarm system is air operated and monitors the change in pressure on the mat when an individual gets out of a chair. This can be invaluable in alerting staff or carers to an individual who is unaware of the risks that getting up can represent. Typically these are people with reduced cognitive function or dementia. The Mat alerts the moment an individual get’s out of the chair.