Advances in sensor technology have mirrored the advances in the silicon industry. As processors become smaller, sensors have become smarter and have increased sensitivity and functionality. Consider using an analog device such as a temperature sensor or flow sensor with a 4-20 mA output. Connect it to one of today's smart relays. Used in conjunction with the wireless switch system, you now have the ability to use the output of the sensor to control a device such as a PLC, conveyor, alarm, lighting, valves, gates, or any other device that needs to be remotely switched based on the output of a sensor. The advantage is the ability to control your device at a distance of up to five miles without having to run wires.