There are a variety of options for detecting door entry into shops and offices.
Shop Bell - a traditional bell-on-a spring, attached to the door to alert entry. see item 62503 and 62503BN
Mini Entry Alarms:
All these products will sound at the position that they are placed.
MA3 - Alarm or chime sounds when magnetic contact is separated and is mounted on the door frame.
MA4 - Similar to the MA3 but has a Keypad Control.
MA5 - Sounds a chime or alarm sound when a movement is detected. Mounts on a nearby wall and is Keypad Controlled.
MA6 - Similar to the MA5, but with a keyfob controlled on/off.
MA7 - As the MA6 but with the addition of magnetic door contacts.
Infrared Door Sensor Beam Chime
SC20W - Place this kit at a doorway. One unit sends an infrared signal and the other unit receives the signal. If the beam is broken when somebody comes in, then the receiver unit will chime (or alarm if required).
Wired Shop and Office Entry Bell Kits: These are kits that use over-door reed switches to make the contact for the bells to ring