Detect Clam

For the duration, you can sense the presence and location of clams within 30 feet of you.

The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, 3 feet of wood or dirt, and any amount of salt water.

It also requires the use of a single clam, which it will always detect.

... It is not a very good spell.