As I we are using Bluetooth for our project it seems prudent to say a little bit about it.

Bluetooth is a wireless protocol for exchanging data over short distances from fixed and mobile devices.

Going into the technical details, “Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the data being sent and transmits chunks of it on up to 79 frequencies. In its basic mode, the modulation is Gaussian frequency-shift keying (GFSK). It can achieve a gross data rate of 1 Mb/s. Bluetooth provides a way to connect and exchange information between devices such as mobile phones, telephones, laptops, personal computers, printers, Global Positioning System (GPS) receivers, digital cameras, and video game consoles through a secure, globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency bandwidth. The Bluetooth specifications are developed and licensed by the Bluetooth Special Interest Group (SIG). The Bluetooth SIG consists of companies in the areas of telecommunication, computing, networking, and consumer electronics.”

Infact everything you will ever want to know (most likely not alot) about Bluetooth can be found here.

A key thing of interest for me from this are the different power classes which would have a significant effect on how good at detecting phones we can be.

“In most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to a pure class 2 network. This is accomplished by the higher sensitivity and transmission power of Class 1 devices.”

So using a Class 1 adapter would be better even if most mobile devices only use a class 2 or 3.

EDIT: After looking into it, it should be very easy to get one of these class 1 bluetooth adapters with 100m range and cover an entire street, including cars passing through.