The secret lies in small biodegradable tabs which are part of a simple plastic mechanism to unscrew the cap.

The tabs degrade by the expiry date, after which any attempt to unscrew the bottle's cap simply breaks them. That causes the cap to turn freely without unscrewing, thus locking the drugs in.

The gadget has been patented by the University of Salford in northwestern England, and a local company, Tacit Technology.

Unused medicines left lying around the home can pose a threat for children and, if used beyond their expiry date, may lose their effectiveness, thus posing a risk for the person taking them.

SPACE.WIRE