least in part under the force of gravity to its first position in which the flap is disposed in substantially vertical orientation optionally such biasing of flap 11 to its first position may be implemented or enhanced with a suitable spring arrangement not shown the flap 11 carries a pad 14 on its rear face adjacent mounting screw s 13 and a bumper 15 proximate an end of the flap remote from that normally located substantially adjacent keynote 32 a schematic circuit diagram for the warning device of the invention is illustrated by way of example in fig2 the indicator circuit 40 includes a first lead wire 41 which is connected at on end to the lock 30 and at the other to one of the poles of a battery 43 a second lead wire 42 connects the opposite pole of battery 43 through an alarm or indicator device 44 such as an audible bell or buzzer 44 and or a light not shown to the displaceable contact means 10 the flap 11 accordingly functions in the manner of the commutator of a switch for alternately opening and closing o completing the series electrical circuit shown in fig2 to operate the alarm 44 preferably the battery 43 and the alarm device 44 are contained within the housing 50.