Ultra-wideband (UWB)
Not RFID, not Bluetooth — a radio that measures distance by timing light, so your car knows you're really at the door.
Ultra-wideband is the odd one out on this site. It isn't UHF (ultra-high frequency), and it isn't passive: both ends have batteries. It's here because it has quietly become the third radio in phones, next to NFC and Bluetooth, and it's moving into door locks and car keys.
#Wide, short and quiet
Most radios pick one narrow frequency and wiggle it. UWB sends extremely short pulses, around two nanoseconds long, that smear across at least 500 MHz of spectrum, somewhere between about 3 and 10 GHz. Phones mostly use channels near 6.5 and 8 GHz.
The trick is that it's very quiet. Regulators cap UWB at a power density so low it sits around the noise floor of other radios, so it can share spectrum with Wi-Fi and everything else without bothering them.
#Why short pulses = distance
A sharp pulse has a sharp arrival time, and radio travels at the speed of light: about 30 cm per nanosecond. Time the round trip well and you know the distance:
- Distance to about 10 cm, by time of flight.
- Direction, too: a device with two or three antennas compares when the pulse hits each one (angle of arrival). That's how a phone's "precision finding" arrow points at a lost tag.
#Why access control cares: relays
Bluetooth estimates distance from signal strength, and signal strength can be faked. Keyless car entry that judged "is the key nearby?" that way has been fooled by relays: two devices passing the conversation between a car on the drive and a key inside the house.
UWB measures time, and a relay can only add delay, never remove it. Nothing travels faster than light. Since IEEE 802.15.4z (2020), UWB ranging also scrambles its pulses with a secret sequence, so a relay can't fake an early arrival either. That's why car keys (CCC Digital Key) and door standards like Aliro use UWB for hands-free entry.
#Where you'll find it
- Phones: recent high-end iPhones, Samsung Galaxy and Pixel models.
- Item trackers, for the "warmer… warmer…" arrow.
- Car keys and newer smart locks.
- Factories, warehouses and hospitals, as indoor positioning: battery tags on people and equipment, located to within centimetres.