Watchdog

Area 
When cast around an area, this spell warns the caster of anyone or anything crossing with hostile intent. If the caster is asleep, he wakes instantly without being stunned. The spell is not destroyed if triggered; it lasts until its natural expiration.

Duration: 10 hours. 
Base cost: 1 to cast. 1 to maintain. 
Time to cast: 10 seconds. 
Prerequisite: Sense Danger.

Item 
Can be cast on an area of floor or ground, or on a rug.  
Energy cost to create: 200 per yard of radius.