Used against the IRA:

One of the most interesting operations was the laundry mat [sic]. Having lost many troops and civilians to bombings, the Brits decided they needed to determine who was making the bombs and where they were being manufactured. One bright fellow recommended they operate a laundry and when asked “what the hell he was talking about,” he explained the plan and it was incorporated — to much success.

The plan was simple: Build a laundry and staff it with locals and a few of their own. The laundry would then send out “color coded” special discount tickets, to the effect of “get two loads for the price of one,” etc. The color coding was matched to specific streets and thus when someone brought in their laundry, it was easy to determine the general location from which a city map was coded.

While the laundry was indeed being washed, pressed and dry cleaned, it had one additional cycle — every garment, sheet, glove, pair of pants, was first sent through an analyzer, located in the basement, that checked for bomb-making residue. The analyzer was disguised as just another piece of the laundry equipment; good OPSEC [operational security]. Within a few weeks, multiple positives had shown up, indicating the ingredients of bomb residue, and intelligence had determined which areas of the city were involved. To narrow their target list, [the laundry] simply sent out more specific coupons [numbered] to all houses in the area, and before long they had good addresses. After confirming addresses, authorities with the SAS teams swooped down on the multiple homes and arrested multiple personnel and confiscated numerous assembled bombs, weapons and ingredients. During the entire operation, no one was injured or killed.