So since about 2007, traffic engineers have begun to take advantage of that fact that cellphones equipped with Bluetooth have become ubiquitous.
Like RFID tags, Bluetooth devices can act as transponders, and work well for measuring traffic speed. Unlike RFID, Bluetooth doesn't tell you how many cars are using the street, but it's about a factor of ten or twenty cheaper.
You might think that the embedded GPS devices in the phones, or maybe triangulation based on the cell towers, would be used by carriers, or by Google or Apple, to collect position information and supply it to whoever needed it... but privacy considerations, and possibly business considerations, have prevented that so far.
Traffic speed monitoring using Bluetooth has been demonstrated by hobbyists as well as universities and state departments of transportation in Maryland, Minnesota, Oregon (PSU and OSU), Texas, and Washington State. Caltrans even has a nice web site about their use of the technique. Commercial systems are offered by a surprisingly, exuberantly large and growing number of companies. There are even kits for building traffic monitoring networks.
The August 2010 issue of Traffic Technology Today has an article discussing the rise of this technique.
There are papers discussing its use for measuring bicycle travel time and pedestrial tracking.
There are even papers discussing optimum placement of Bluetooth detectors.
Consumers can set their phones to "Undiscoverable" (and Android phones are undiscoverable by default), in which case the phones no longer respond to Bluetooth inquiries. The addresses of discoverable phones are, like the addresses of public WiFi access points, considered public information, but nevertheless some caution is recommended when handling this data, as previous wireless monitoring efforts have raised privacy concerns. For example:
Here's what a few government agencies say about related questions:
... Data use and retention policies: ... Destroy any base level MAC ID information after processing. ... Use industry standard encryption and network security. ... Randomization and/or encryption of the data at its source: ... Encryption / Truncation ... above methods are implemented in the sensor, not at the central processing. By implementing randomization measures at the detector, it becomes physically impossible to obtain the complete and globally unique MAC address, further protecting privacy.
Blue Motion is consistent with the Canadian privacy commissioner's "Privacy By Design" requirements. Blue Motion Bluetooth receivers track only the unique randomly generated MAC address (device ID). They do not read phone numbers. Nor do they read the Bluetooth transmissions (e.g., between a headset and a cell phone). The Bluetooth receivers only detect the presence of a signal and the unique device MAC address. To further ensure the individuals privacy and anonymity, the leading digits of the MAC address are deleted.
The MAC addresses read by AWAM are not directly associated with a specific user and do not contain any personal data or information that could be used to identify or "track" an individual's whereabouts. In addition, all addresses collected by AWAM are anonymized through encryption immediately upon receipt. Users who have privacy concerns are also able to turn off the Bluetooth discovery function of their device which prevents it from being read by AWAM at all.
You can send us your Bluetooth MAC-address via our Opt-out page. Once we receive this, we will exclude your data from any further research activity and delete any data we already hold. It may take us a few days to action this request.There is a big "Opt Out" button right below that text.
Here's a first cut at a list of guidelines for Bluetooth monitoring:
Someone's even tried doing it with Arduino.
Using an external antenna may help. USB Bluetooth units with a jack for an external antenna are a bit hard to find. Here are a few:
From a second story window, watching for a G1 phone held by someone walking down the sidewalk, the range of an Azio class 1 dongle (with internal antenna) was about 20 meters, of a Parani UD100 dongle with a 1db stub antenna was about 35 meters, of a Parani UD100 dongle with a 5db dipole antenna was about 50 meters.
KMZ file showing paths detected using above data