The present invention describes a RFID tag and a system and method involving a plurality of RFID tags. Each RFID tag is attached to an object (or to a structure or a person) on which the presence of a predefined fluid is monitored. In a first state, (absence of the monitored fluid), the tag is acting as a passive RFID tag, and the information it holds, (at least its identifier—ID), can be read with a proximity reader (a hand held or stationary/fixed reader). This operation is performed when the RFID tag is attached to the object (or person) to be monitored. At this stage a table associating tag ID, object name (or person name) and location (or any other information), may be built, and may be recorded so that information it contains is accessible by a control center. In a second state, whenever the monitored fluid appears on the tagged object, a fluid activated battery generates the electrical power which is used to power the RFID tag. The RFID tag then acts as an active RFID tag and starts to emit messages (an alert for instance) which can be received by a distant RFID reader. Alert messages include at least the tag ID but may comprise additional information like a name or a location.