There were No Secrets in Madrid

Several centuries ago, in Spain, there was a great distrust of locks. To be safe, the householders of a block hired a watchman to patrol the neighborhood and carry the keys to their dwellings. To enter or leave a house, the resident clapped his hands vigorously to summon the watchman with his key, so, all comings and goings became a matter of public record and there was little chance for "hanky panky" in old Madrid.