Smoke alarms contain incomplete summoning circles and a mana crystal. When smoke enters the chamber, it's manipulated with pipes so as to complete the summoning circle. The summoning circle then proceeds to use the mana from the crystal to call forth a daimon, which screeches to alert the home owners of the fire. When the home owner blows the smoke away, this breaks the summoning circle, sending the daimon back to the spirit world.