The Blue Meanies use really freaky looking clowns (known as "Countdown Clowns") as an alarm system. They've got no arms and really do look horrific. The noise they make when they're alarmed REALLY doesn't help. Plus when things tend to explode when you press their squeaky noses.
If they see an intruder their heads spin round and round and they go 'AAAAAWAWAWAAAAERGH!' repeatedly until someone comes to kill the accused, who is normally paralysed with fear at this point. They also create random explosions in different places when people press their noses.