You buy a cellphone from a private seller online. But when you try to activate the phone, you find you’re out of luck.

The wireless carrier tells you the phone is on a blacklist, since it was stolen or used for fraudulent activity. Your only choice is to buy a new device.

It’s a terrible dilemma that can confront you when looking for a deal on a used phone. And until this week, you couldn’t check out a potential purchase to see if it was reported as lost or stolen.

Now you can find out if a phone is blacklisted before buying by using the Canadian Wireless Telecommunications Association’s website, ProtectYourData.ca.

On the home page, go to a yellow square: “Check the status of your device in Canada.” Scroll down to a blue oval, where you can click to check the IMEI number. (IMEI stands for International Mobile Equipment Identity.)

Once you enter the 15-digit unique identifier, you should get a message that says: “Your device has not been reported lost or stolen and is not currently on the national blacklist.”

What if you find that a phone’s IMEI number is on a national blacklist?

Count yourself lucky. You can back out of the deal before trying to activate a wireless device with a questionable past.

Canada is the first country to add a consumer lookup feature to its database of lost and stolen phones, says Marc Choma, an association spokesman.

The service is limited to two queries a day. But you can bypass the cap by using a different device to search (as I did after botching my first few tries).

The IMEI number can be found on the white label underneath a device’s battery — but you probably need a magnifying glass to see the tiny print. Or you can find it by entering *#06# on most devices’ phone keypads.

Is there a major problem in Canada? Why do we need a national blacklist?

Industry statistics show that there were 496,000 lost and stolen phones in 2010, compared to 420,000 in 2011 and 263,000 in the first nine months of 2012.

The decline may be attributed to consumers buying more complex and costly smartphones equipped with apps to locate their whereabouts if they vanish.

Still, despite the trend to fewer losses, Canadian police are concerned about public safety. They urged the industry to find a solution that would reduce the violence that often accompanies mobile phone theft.

Canada’s telecom regulator also wanted to see an industry response, citing privacy concerns that arise when consumers lose confidential data stored on a mobile device without a password lock.

The Canadian Radio-television and Telecommunications Commission encouraged wireless carriers to join an international registry that already existed and start a public education campaign to help consumers protect themselves against theft.

A year after the issue was identified as serious, Canada’s wireless industry is participating in a list of stolen and lost U.S. devices maintained by the GSM Association (GSM is a popular wireless format).

Devices with the CDMA format, a technology used by Public Mobile, do not have an IMEI and are not included in the database.

“It is imperative that consumers contact their service provider to immediately report a lost or stolen phone to have their device deactivated,” the association said in announcing the new registry on Sept. 30.

“It is only when the device has been reported that the service provider can then add the device to the blacklist. All instances of personal theft should, of course, be reported to local law enforcement as well.”

At its public website, the industry has tips on protecting yourself from harm when on the go:

Don’t send text messages or talk on the phone while walking.

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Be extra attentive at places where phone theft is likely to occur (parks, transit stations, parking lots and automated banking machines).

When using an electronic music player, keep the volume low and understand that earphones may identify the type of device you’re using, making you a target for thieves.