Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
G04C21/00—Producing acoustic time signals by electrical means
G04C21/16—Producing acoustic time signals by electrical means producing the signals at adjustable fixed times
G04C21/30—Producing acoustic time signals by electrical means producing the signals at adjustable fixed times with provision for a number of operations at different times, e.g. ringing the bells in a school