ADT Corp. is locking up a bigger piece of the Canadian security monitoring market, spending $555-million to buy Reliance Protectron Inc. to add 400,000 home and business customers.

Protectron will remain based in Montreal and will keep operating under that name, while ADT’s existing Canadian operations will retain the ADT brand. Florida-based ADT said that “as it strengthens its Canadian focus” some administrative functions that have been run from the U.S. will be moved to Canada.

The companies are similar in size in Canada, each employing about 900 people here, and the transaction will roughly double ADT’s Canadian customer base.

“We think they have a great management team and I just think it was a perfect fit,” said ADT chief executive officer Naren Gursahaney.

The companies are both in the business of wiring homes and businesses with sensors that can detect burglars, blazes or other hazards. The detectors are connected to monitoring centres, which can get in touch with residents or emergency personnel to alert them to trouble. The companies are increasingly providing systems that also enable customers to control their security systems and other home functions remotely.