Entrusted device localization scheme using ultrasound signatures

The disclosure generally relates to a localization scheme that may use ultrasound signatures exchanged among entrusted devices to locate lost or otherwise misplaced devices. More particularly, a user device may initially exchange an ultrasound signature or other inaudible audio signature with an entrusted device (e.g., during a pairing procedure with the entrusted device) and subsequently search an ultrasound domain in response to detecting an inactive state (e.g., based on measurements that indicate inflicted motion or processor activity). As such, in response to detecting the initially exchanged ultrasound signature in the ultrasound domain, which may be emitted from the entrusted device or an unpaired device that has been authorized to emit the ultrasound signature, the user device may generate an audible or visual notification in a user domain and optionally further enable more sophisticated user notification and localization tasks to assist in locating the user device.