Methods and systems of detecting objects in proximity to user devices and distinguishing between object types are described. One method includes measuring a magnitude of mutual coupling between two antennas of the user device using a transmitted signal by a first antenna and a received signal by a second antenna. The method distinguishes between the user device being proximate to free space, a first object type or a second object type using the magnitude of mutual coupling or magnitude of received signal strength. The first object type includes non-water-based objects that do not absorb electromagnetic radiation and the second object type includes objects that absorb electromagnetic radiation.