This signal jammer was offered for sale on eBay for use in blocking a narrow range of electronic frequencies. (eBay)

An increasing number of criminals are using widely available technology to block police communications, according to police.

The devices — known as jammers — can create dead zones where police radio and cellphone transmissions are disabled.

The jammers can be bought on dozens of websites for between $100 and $200, according to Abbotsford police Const. Ian MacDonald.

The devices can create a communications-free zone up to 200 metres in diameter, which can interfere with police operations such as the execution of search warrants, MacDonald said.

Handheld units can deaden a zone about 20 metres wide, he said.

Most devices illegal

"It's a reality in the policing world," MacDonald said of the new technology.

"Dependent on how many of these ultimately make it to market and ultimately are purchased by consumers, it may become more of a reality for us."

Abbotsford police believe a number of the units are in use in the community, but they have not yet seized any, MacDonald said.

Macdonald said a particular concern is police safety in situations where an officer might be calling for backup or help but cannot communicate with others.

Frequency-blocking equipment that is not sanctioned by the federal government is illegal to own or operate in Canada, according to the Radiocommunication Act.

With files from the CBC's Meera Bains