A building system includes a communication network, a plurality of wireless nodes, a plurality of passive wireless devices, and a processing circuit. The plurality of wireless nodes are disposed within a building operably and are coupled to the communication network. Each of the passive wireless devices is affixed to or within an object within the building. At least some of the objects constitute fixtures within the building. Each passive wireless device contains first information regarding at least one property of the object, and is configured to communicate wirelessly to at least one of the wireless nodes using power derived from communication signals detected in the passive wireless device. The processing circuit operably is coupled to receive the first information from the wireless devices, the processing circuit configured to update a model of at least a portion of a building based at least in part on the at least one property of the objects.