Abstract: This invention relates to a device for detecting a fall of level of flowable material in a closed container by emitting an oscillation. It is electronic in nature and the circuit has an amplifier with a feed-back terminal that is connected to a feed-back network. The feed-back network in turn includes two vertically spaced apart identical probe condensers each having an open dielectric space and each being in different feed-back paths of the feed-back network. The feed-back network is activated as the level of the flowable material drops, whereby the difference in the dielectric material of the condensers provides a change in input current to the amplifier. The circuit is responsive to a positive change in input current to cause the amplifier to commence oscillation on dropping of the level past the condensers to signal the drop of the level of the flowable material. The device is stable in design, low in cost and easy and reliable to use.