(a+ 1/N) (1 1/99Na+1) +Z /1?9(Na+1) = a false alarm

There was a time when a burglar alarm went off that a bobby would have arrived to see what was up. Now it is the subject of a mathematically based police investigation of Pythagorean proportions.

Angered by waste caused by 1 million false alarm calls a year, the police have turned to a statistician to identify inefficient installers. The piece of algebra he devised (shown above) is said to be infallible. By entering the number of false alarms into the equation, police believe they can nab rogue installers.

But the proposal has set off a clangour of disapproval in the alarm industry, which said firms could be unfairly put out of business. Almost all false alarms which trigger an automatic police response are caused by the errors of owners, who can already be blacklisted under the police's "four strikes and you're out" false-alarm rule.

Yet if the new formula identifies an installer as having an unusually high number of false signals, the police say they will refuse to work with the firm.

Nigel Craig, of Eurotech Security Systems, in north London, complained to the Metropolitan Police after receiving an explanation of their proposed use of the formula. "I have not the foggiest as to what you are talking about," he wrote. "I can only assume some people have nothing better to do or this is part of a conspiracy to improve the income of my psychiatrist."