... cleint press button with their need ,the message will be sent to the receicer .uopn receive of ... bed No. and ring .then the waiter will go for service . Feature :1.high strength aluminum alloy cover2 ... indicators show different servie type ,one indicator for service ,two for order ,three for bill 6.the ... ther are two call infors and the display will show 2.Technical Parameter:Working voltage:DC12V-DC24V ...