Strange White Box in New Apartment
Inovonics Wireless   SKU: EN1723
  
  The Inovonics EN1723 provides internal measurement and external thermistor options in a single device. The on-board sensor is excellent for monitoring ambient indoor temperature, and the external sensor is user selectable to match your application.


(source)

Like Tyson notes, these are used in zoned systems.  The receiver should be located near your equipment: presumably a larger white box; most likely with the name Inovonics on it. 

These are wireless; should you ever have a problem with a single zone, check their batteries first.