Abstract: A toilet reservoir fill alarm including water level sensors which can be positioned in the water reservoir tank of a flush toilet to detect the presence or absence of water at a desired level. A switch responds to the water level sensors and produces a control signal during the absence of a desired level. The control signal operates a timing circuit in order to produce an output signal at the termination of a predetermined time interval. Responsive to the output signal is an alarm circuit. In this manner, an alarm will sound should the toilet tank reservoir not refill during the predetermined time interval following the flushing of the toilet.