Travellers may have to bare it all now that the government has announced plans to install dozens of scanners that can peer through clothing at airports across Canada.

An airport watch system will also be set up to look for suspicious passengers and tab them for further screening.

"We've got to stay ahead of the terrorist elements," Transport Minister John Baird said Tuesday in announcing plans to buy 44 of the $250,000 machines.

The announcement was part of an international response to a Christmas Day attempt by a Nigerian man to blow up a jetliner over Michigan by igniting explosives sewn into his underwear.

"We must remain vigilant," Baird said.

The United States has already demanded tighter screening of passengers from 14 countries, including Nigeria. Canada has banned certain types of carry-on bags for U.S.-bound air passengers.

Baird and other government officials couldn't say whether passengers from the 14 countries on the U.S. list will face more checks at Canadian airports.

But Prime Minister Stephen Harper said it's not a given that his government will follow the Obama administration in lockstep.

"We're going to take a look at these measures and we may arrive at different conclusions," he told the CBC on Tuesday.

"The one concern I do have about all of this -- and I've expressed this to American leaders -- I see what I call the 'gun registry' approach to a lot of security issues.

"Which is, let's just put everybody on a list, register everything. And we know from our own experience with our gun registry that this is not necessarily the smartest and most effective way to actually identify real threats.

"So it's my hope as we look at these things, which invariably will cause some changes in mass procedure, that we make sure that we respond in ways that are intelligent, ways that effectively identify threats before they happen. As opposed to simply massive bureaucratic sets of rules."

The Christmas day incident has sparked intensified security measures around the globe even though it appeared to be the result of a failure in American screening measures alone.

But Harper said Canada and the U.S. face "common threats."

"I wouldn't want to say that what happened there could not happen here. And obviously if they're going to undertake steps to address that kind of threat in future, we're going look at those threats and examine whether we should take similar measures."

Harper said the need to protect air travellers must be balanced against privacy and equality rights, keeping in mind that Canadian courts tend to be "less deferential" to government on security matters than American courts.

Britain also wants to deploy the scanners at its airports, but the government has run into opposition over privacy concerns. Canada's privacy commissioner doesn't share those worries.

Baird and Rob Merrifield, minister of state for transport, said the scanners will only be used for passengers singled out for secondary screening. And people who don't want to go through the machines can choose to be frisked instead.

The scanners will first be installed in Vancouver, Calgary, Edmonton, Winnipeg, Toronto, Montreal, Ottawa and Halifax and will all be in place in by spring.

The machines produce a three-dimensional outline of a person's naked body, allowing screening officers to see whether someone is carrying plastic explosives or other dangerous items.

Privacy campaigners and children's rights groups in Britain say the technology violates British and European laws by producing sexually explicit images of children.

Baird said children under the age of 18 won't have to go through the scanners at Canadian airports.

Canada's privacy czar gave the devices her blessing last fall after the national air security agency allayed concerns she had about them.

Under the plan approved by the privacy chief, the officer would view the image in a separate room and never see the actual traveller. Only people singled out for extra screening would be scanned, and they would have the option of getting a physical pat-down instead.

Merrifield said the images will automatically be erased after the scan. No copies will be made or kept.

Chantal Bernier, assistant federal privacy commissioner, told a conference late last year that the holographic image generated by the scanner makes it difficult to identify the traveller's face.

"You would not know who it is, even if you knew the person was in line," she said at the annual meeting of the Canadian Association for Security and Intelligence Studies.

In addition, the image would be deleted the moment the person leaves the screening portal.

"In our view, these privacy safeguards meet the test for the proper reconciliation of public safety and privacy," Bernier said.

The scanners are already in use at airports in cities including Amsterdam, Moscow and Phoenix. They are also found in the high-security "green zone" of Baghdad and at some U.S. courthouses and prisons.

Bernier added that the Canadian Air Transport Security Authority had done thorough threat assessments that revealed a need to search passengers for weapons that might elude a conventional metal detector.

The privacy commissioner's office recommends a public education campaign to explain the machines, and says minors would be scanned only with the consent of guardians accompanying them.

The air security authority says the low-level radio frequency wave emitted by the body scanner meets Canadian health-and-safety standards.

The national air security agency tested the full-body scanners in British Columbia at the Kelowna airport between June 2008 and January 2009.

A report on the Kelowna pilot project endorsed the technology for wider use.

But the agency's report, prepared last spring and obtained by The Canadian Press under the Access to Information Act, found shortcomings.

The scanners take longer than a physical pat-down to process passengers, and they blurred parts of the body they weren't supposed to.

The agency says the wonky blurring feature could make it difficult for screening officers to spot dangerous contraband.

"The results indicated that the (blurring) feature was not precise in the image blurring placement on the passenger and could, at times, blur areas that must be reviewed by the screening officer," the report says.

"This could allow for items to be concealed in these areas defeating the benefits of this technology."

The report recommended against using the blurring option. Ron McAdam, a spokesman for the Canadian Air Transport Security Authority, said Tuesday the images would not be blurred.

Last week, Canadian transport officials said there were no plans to speed up consideration of the long-discussed scanners in light of the near-disaster in Michigan.

But the government, under pressure to respond to the dramatic U.S. incident, has decided to make the multimillion-dollar purchase.

"We are ensuring that Canadian officials will have the tools to do the job," Merrifield said.

New Democrat transport critic Dennis Bevington called the purchase of the scanners a "knee jerk" reaction to the failed U.S. terror plot.

I don't think they've made the case that these things are necessary," he said. "I think they're acting in a very quick fashion ... to a situation that occurred over Christmas."

Liberal Senator Colin Kenny, who chairs the Senate defence committee, said he has concerns the scanners will add to the wait times at airports. He also called for more screening of airport workers.

Those in the airline industry welcomed Tuesday's announcement.

George Petsikas, president of the National Airlines Council of Canada, said he's anxious to see the scanners in action.

"We've heard about it. We've read about it. Now we want to see it," he said.

"If indeed they live up to their billing, I think you'll see us basically saying, 'Great. Let's work on this."'

Some travellers were looking forward to an alternative to a frisking.

Lorraine Williams, a 66-year-old grandmother, said she makes frequent trips between Calgary and Vancouver Island to visit her 94-year-old mother. She said she has been singled out for a pat-down on two of her last four trips.

"I would much prefer having a scan than have somebody patting down the side and top of my bra and having to bend over while someone puts their hand inside my pants waistband," she said in an email.

"Enough said."