Mobile device with ultrasound ranging

A ranging system comprising:

• a first device including at least a first ultrasound transmitter and one or more ultrasound receivers;
• and
• a second device proximate to the first device, the second device including at least a second ultrasound transmitter,
• wherein the first ultrasound transmitter is configured to transmit a first signal toward the second device;
• wherein the second ultrasound transmitter is configured to transmit a separate second signal to the first device in response to the first signal from the first device;
• wherein the one or more ultrasound receivers are configured to receive the separate second signal from the second device;
• and
• wherein the first device is configured to determine a range of the second device based on at least the second signal.

A method of finding a range of a proximate device, comprising:

• transmitting a first ultrasound signal from a mobile device ultrasound transmitter;
• recording a time of transmission of the first signal;
• receiving a separate second ultrasound signal from a proximate device at a plurality of ultrasound receivers of the mobile device, the separate second ultrasound signal being received subsequent to transmitting the first signal;
• recording times of receipt of the second signal at the plurality of ultrasound receivers;
• and
• calculating a range between the mobile device and the proximate device and a relative orientation based on time lapses between the recorded time of transmission of the first signal and the recorded times of receipt of the second signal.