Certain aspects of the present disclosure provide object detection based on perturbations in a channel model over time. An example portable apparatus includes a primary antenna, a secondary antenna, a transmit path, a radio frequency (RF) coupler, and a receive path. The transmit path is coupled to the primary antenna and configured to output a transmit signal for transmission via the primary antenna. The RF coupler is coupled to the secondary antenna. The receive path has an input selectively coupled between the transmit path and the RF coupler such that when the receive path is coupled to the RF coupler and configured to operate concurrently with the transmit path, the receive path is configured to receive a reflected portion of the transmit signal from an object located in proximity to the portable apparatus.