With fail-safe circuit that engages when input power drops below 3 Vdc, U004E Ultrasonic Gap Switch anticipates power loss to level sensing devices to aid monitoring of oil fields spanning miles of remote regions. Switch is customized to end-user's desired output in NO or NC states. When power supply drops, unit can open valve, turn on pump, or send alarm to alert technicians. Other features include glass to metal seal construction and 316 stainless steel or hastelloy c material options.