A wireless sensor preferably has a case which is intrinsically safe and has no exposed parts which can become not intrinsically safe due to the passage of time or through contact with chemicals typically encountered in a location where the wireless sensor is used. It preferably has no integral visual display other than lights, and it preferably includes at least one signal light. The sensor preferably includes a wireless transceiver for allowing remote read and remote control of the sensor. The sensor preferably includes piezoelectric pressure detectors for allowing a user to locally interact with the sensor by pressing on the case. Data can be automatically harvested from the sensors by a portable electronic data-retrieving device which is usually geographically remote from the sensors when the portable electronic data-retrieving device and the sensors are in range of a wireless system which allows them to communicate when they are geographically proximate each other.