An active tag can communicate with other active tags with or without the
presence of an interrogator. It does not communicate with passive or semi-passive
tags. An active tag can be designed to broadcast its data using broadband or
spread-spectrum technologies to enhance its data communication performance.
It can be set to a sleep mode in which it uses only a small amount of
power and does not transmit data.When it receives a specific signal, it awakens
and transmits its data. This reduces the power usage from the battery and extends
battery life. Some active tags work at two different frequencies. At the
lower of the two frequencies, they work in receive only mode and use this mode
to receive a signal from a nearby transmitter. This signal awakens the tag, and
then the tag transmits its data at higher frequency and longer range.During this
transmission, it may also transmit the identity of the device that awakened it.
This is typically used within a large container yard where you want to track the
movement of the container fromone zone to another. The tag may also be set to
transmit a periodic beacon to let an interrogator know of its existence or send
the signal when moved or handled. It can even send a low battery alert. The US
Department of Defense has been using this type of tag for many years