In a recent case in the United States Supreme Court, the Justices wrote that government surveillance of one’s public movements for twenty-eight days using a GPS device violated a reasonable expectation of privacy and constituted a Fourth Amendment search. Come so soon after Edward Snowden’s revelations about NSA surveillance, it has caused privacy groups to look more closely at the use of ICT.

Kevin Bankston, Policy Director of the New America Foundation’s Open Technology Institute, co-authored a paper with independent researcher Ashkan Soltani for the Yale Law Journal. Their paper, “Tiny Constables and the Cost of Surveillance: Making Cents Out of United States v. Jones” sought to quantify the cost of surveillance in the mobile age, and to stimulate debate about US constitutional rights.

To start with, they looked at traditional surveillance costs. In their model, the primary cost of foot pursuit is the salary of the agent. An FBI agent’s total salary is approximately $130,000 per year, so they have estimated the hourly “pay cost” for an FBI agent to conduct surveillance on foot to be $50 per hour. Covert foot pursuit with five agents (a standard operational model) is therefore $250 per hour. The use of a car in a pursuit adds about $5 per hour, so that five agents in five cars would cost about $275 an hour.

Now for the tech. Mobile phone tracking using a simple IMSI Catcher or ‘Stingray’ as they are known in the US works out at $105 per hour – due to the cost of buying it in the first place. Thereafter, costs are negligible.

For GPS tracking, the monthly fee to hire the unit, plus two hours of salary for each of two agents to install and uninstall the device, brings the average cost of GPS surveillance to $10 per hour (falling to as low as $0.36 per hour if used over a 28 day period).

Finally, there’s mobile phone tracking with carrier assistance. Rather than pursue a suspect in the field, law enforcement agents can track subjects by following the signal of their mobile phones by obtaining location information from the network operator. According to data gathered by the American Civil Liberties Union, phone companies provide this data to law enforcements at varying rates: as of August 2009, Sprint charged $30 per month per target, AT&T charged $25 a day plus an upfront $100 fee, and T-Mobile charged a huge $100 per day. Put another way, the estimated hourly cost for operator-assisted mobile phone tracking ranged from $1.25 to $5.21, although these prices would fall if tracking was required over a longer period (and they are based on 2009 numbers, so are no doubt lower today).

What this boils down to is that the cost of using communications technology surveillance is many orders of magnitude cheaper than using the old-fashioned ‘human’ approach. At the extreme case, the authors have calculated that, even using the most expensive rates, it is 53 times cheaper to use carrier assisted mobile phone tracking than it is to deploy a five-car FBI team.

That saving could be used to reduce the budgets of the law enforcement agencies in our age of austerity – but equally it could be used to deploy many more surveillances, 53 times more in fact.

And there’s the concern.

“Our contribution is the suggestion that dollar cost can be a key metric for judging when a radical shift in police power has occurred. With location tracking as our example, we’ve detailed the precipitous drop in cost between old and new surveillance techniques,” wrote the report authors. “When highly revealing surveillance of a citizen’s activities is possible for pennies a day, we need the Fourth Amendment to protect us. Otherwise, we may soon live in a world of unlimited virtual ‘tiny constables’ monitoring our every move.”