This optical level sensor from Sensata Cynergy3 accurately detects the absence or presence of liquid. It's designed for single-point liquid measurement and chassis mounts externally onto a tank for ease of installation.
The sensor is reliable as it resists false triggering caused by foam on the surface of a liquid. This significantly reduces the chances of it giving you an incorrect alarm. It uses an infrared emitter and detector for precise level detection. A switch like this one is commonly used in small-scale installations such as vending machines.

• Maximum pressure of 7 bar for use in high-pressure systems
• Impact and chemical-resistant polysulfone body for durability
• Wide operating temperature range of -25°C to +80°C for use in demanding environments

You can clean this optical sensor with an alcohol-based solvent. Chlorinated solvents may damage the device's housing and are therefore not recommended.

This versatile, general-use sensor can measure any liquid medium that's compatible with polysulfone, including most acids and alkalis.