Intruder Charm

The Intruder Charm detects intruders and sounds an alarm.Horace Slughorn used it on a temporary Muggle-owned house he was living in, allowing him to detect Dumbledore and Harry as they approached in Harry Potter and the Half-Blood Prince.It is possible that Alastor Moody was using it in 12 Grimmauld Place to set off charmed dustbins (which spewed litter at intruders) if there was an intruder on the property.