Arcane Sensor

 You create an invisible, magical eye that can be attached to specific item such as a stone or the branch of a tree, or on the shaft of an arrow. It remains attached to whatever you cast it on.  For example, if it's attached to a stone, you can throw that stone across a river and the arcane sensor would stay attached to it. It remains invisible in the place you cast it until it is triggered or it is dispelled.

The eye has a 30 ft radius alarm that is activated when any creature or designated creatures enter its radius. This sets off an alarm in the casters mind who then can look through the eye for up to 30 seconds or until the eye is dispelled. There is no maximum distance or time for the spell to remain active as long as it hasn't been triggered or is on the same plane. 

You mentally receive audio/visual information from the eye, which has darkvision out to 30 feet. The eye can look in every direction.

The spell can be used once per day but does not renew if there is if it is still in use from the previous day, unless you choose to dispell it in the morning, then you may regain the use for the day.