Methods, systems, and devices for wireless communications are described. A user equipment (UE) may be configured to be positioned in different possible physical configurations and may identify its current physical configuration based on a modem-based sensor. The UE may transmit a signal from a first antenna element and receive an echo of the signal at a second antenna element different than the first antenna element. The UE may then generate an echo signature for the echo of the signal and determine that the UE is in a first physical configuration (e.g., its current physical configuration) from the possible physical configurations by comparing the generated echo signature to a set of echo signatures that correspond to each of the possible physical configurations. Accordingly, based on the determined first physical configuration, the UE may perform an operating system function that corresponds to the first physical configuration.