CRA headquarters in Ottawa

The Canada Revenue Agency headquarters in Ottawa is shown on November 4, 2011. (Sean Kilpatrick/Canadian Press)

A Dartmouth couple got a nasty surprise when they returned home from a month's vacation. It was a threatening voicemail on their home phone.

"Your physical address is under legal observation by Canada Revenue Agency and the Department of Public Safety and Emergency Preparedness," the message said in part.

It was a mechanical voice.

"We had several messages which I thought were a little bit strange," Ralph Waugh said.

"Anybody that's going to survey our house would be comatose with boredom after 20 minutes.  So it's unlikely that Revenue Canada would do that," he added.

Waugh said he wasn't taken in by the phone call, but he decided to speak out to warn others.

"Some other people might take them seriously and call the number and that would probably be bad," Waugh said.

Halifax Regional Police confirm that the threat of home surveillance is a new twist on an old, familiar scam.

"This kind of gives a little more urgency to the person that's on the other end of the phone, the victim of the scam," Const. Phil Power said.

"They're trying to pressure you to send some money immediately to take the surveillance off your home."

The Canada Revenue Agency reminds people on its website that it would never contact taxpayers in this manner.

While the scam is familiar and transparent to most people, not everyone sees through it.

"And we do have several victims out there," Power said.

"We definitely like to remind everyone if you are a victim of this fraud to call us at the Halifax Regional Police and a member of our fraud unit will be assigned."

The threatening voicemail included a phone number with a 613 area code, which is the area code for Ottawa. But when CBC News called the number, it was not in service.

Power recommends that if people do get a call, they hang up and call the number to confirm if it really is from the tax collector.