According to the invention, IEEE 802.15.4a packets are used for communications, ranging and passive radar (detecting changes/motions, tracking objects in the environment) functionality. Changes and motions in the environment are detected by exploiting the specific preamble structure of the IEEE 802.15.4a packets. A sequence of packets transmitted through an environment is received. Each packet includes a preamble. The preamble in each packet is despread to update a reference multipath profile and to obtain a current multipath profile for a currently received packet. The reference multipath profile is compared with the current multipath profile to detect an object in the environment.