Sensors behrotest® for canisters with screw on closures Sensors for monitoring the maximum fill height Sensors for monitoring the maximum fill height are used to protect against damage from overflowing vessels. A float assembly encloses a reed contact which activates an acoustic alarm when the maximum fill height is reached enabling the user to stop further filling in time to prevent overflow. Sensors for monitoring the minimum fill height Sensors for monitoring the minimum fill height are used to protect against interruption in supply or inadequate volume available in processes requiring continuous withdrawal of a liquid from a container. They give an acoustic warning when the content of the container runs low. The sensors are available in various lengths to permit use in containers of different heights. When the liquid level in the container sinks below the set point a float drops opening a reed contact. An alarm warning then informs the user of the imminent risk of an empty reservoir.