You ( who has better things to do) are selling products (in jars or containers) displayed on roadside stand or store stand and through out the day customers come and go. Say the display is small wood stair type with two rows. Battery, bell (lamp) and power switch( probably, key switch ON/OFF would be safer idea) can be locked in back area of display.
Switches can be spring brass with small 1/16 inch brass rod soldered on so container weight holds switch open or use NC switch with plunger long enough to go thorough display case and be held open with weight on top.
Customer will walk up and lift products to look at item closely and the bell will let you know customer has arrived.
