When Calgary Police Service detectives bought a cellphone-spying device, they apparently did so without Ottawa's blessing.

"Acquisition can be done at the municipal level," Inspector Ryan Jepson said in an interview. "We didn't need federal approval to acquire one."

His remarks to The Globe and Mail are the first time that a municipal-police official in Canada has spoken openly about using IMSI-catcher surveillance. The RCMP divulged its own practices last week, and Insp. Jepson said smaller police forces can also be trusted with the technology.

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Read more: RCMP reveals its use of cellphone-tracking machines

The recent statements about police practices in Canada suggest that forces use the devices sparingly and under judicial supervision. But they also indicate fewer central bureaucratic controls in Canada than in the United States, where the Federal Bureau of Investigation and the Federal Communications Commission work together to shape how local police acquire and use IMSI-catcher surveillance.

"The FCC requires any law-enforcement agency that makes use of such devices to co-ordinate such use with the FBI," reads a report released last year written by two leading privacy researchers in Canada.

Yet when the RCMP broke its long silence on IMSI catchers last week, Chief Superintendent Jeff Adam would not speak about what other forces might be doing. "The RCMP does not have a supervisory role on the use of this technology," he said.

It is unknown how many municipal and provincial police forces in Canada have their own IMSI catchers. These portable data-dredging devices work by imitating cellphone towers, and detectives often use them to obtain identifying information from a phone being used by a criminal suspect.

Police had long deflected questions about IMSI catchers for fear of drawing attention to such investigative capabilities, and the privacy problems they pose. Critics point out that every time an IMSI catcher is switched on, it also captures digital data from bystanders' phones in the area being scanned.

But just how revealing is that captured data? Not very, police officials say, adding that IMSI catchers are the police-investigative equivalent of a Hail Mary football pass.

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The Calgary Police Service acquired its device three years ago and has used it for 14 serious-crime investigations over the past two years, said Insp. Jepson, who is in charge of Calgary Police's technical operations section. "It's not Star Wars-ish, where you could turn the device on and see every phone in the city, that's not how it works," he said.

He added that the specific device is incapable of intercepting texts, calls or messages. He said it can only pull unique identifier numbers off phones, such as the international mobile subscriber identity, or IMSI, number.

And these 15 digits do not reveal much about the user.

"For us to go that next step, to acquire the basic subscriber information, or who that IMSI belongs to, we require a search warrant," Insp. Jepson said.

Such orders, when served on phone companies, can yield valuable leads, he said. They can also fizzle.

"We have had cases where we look at the basic subscriber information and we get names like Moe Faux. M-O-E F-A-U-X, because people are able to get devices through [anonymous] prepaid means."

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The RCMP last week described using its 10 IMSI catchers in similar ways.

The surveillance capabilities of IMSI catchers are often said to be constantly improving, so it is unclear how public-safety officials might use more sophisticated versions.

Some glimpses of what might be coming are available now. The Ontario Provincial Police confirmed to The Globe last week that they continue to conduct a criminal investigation into federal prison officials in Ontario. In 2015, these prison officials acquired a powerful version of an IMSI catcher in hopes of finding inmates' contraband phones.

However, the prison warden later apologized to guards for capturing their communications. This admission would appear to put Corrections Canada on the wrong side of federal laws that prohibit the warrantless wiretapping of private communications.

Once acquired, such devices would be subject to the federal Radiocommunications Act, which is enforced by Industry Science and Economic Development Canada (ISED), a federal department.

The act states that anyone who uses a device that interferes with public airwaves will face fines or jail time if they do not get the blessing of regulatory officials in advance.

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However, a spokeswoman for ISED told The Globe and Mail in 2016 that "no such authorizations have been provided to date."

Police are not above this law, and Insp. Jepson indicated that ISED officials now appear to be asserting their enforcement powers over police-issue IMSI catchers. "There was some ambiguity as to whether we required an exemption" to use it, Insp. Jepson said. "It turns out that it seems ISED would prefer that we have an exemption, so we are in that process right now."