This is a very simple circuit consisting of only two components,  a three pin ic UM66 or BT66 and a transistor BC548. this is a very easy method to make a calling bell. the circuit can be made without soldering also. i used a cassette box as outer covering    
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Step 2: Circuit diagram

Picture of circuit diagram
complete the circuit according to the circuit diagram, its very simple circuit and works on two AA batteries, the music will vary according to the IC UM66   

Step 3: Conclusion

hope you enjoy the circuit................ please rate the instructable and comment if there is any doubts.Rechargeable battery should not be used if Speaker resistance is less than 8 Ohm and may burn the Transistor BC548 
Dipankar1 year ago
It is a very good project specially for patients in bed who requires constant attention.
sooraj619 (author)  Dipankar1 year ago
nodoubtman2 years ago
What about a buzzer without the transistor??

thank you!
sooraj619 (author)  nodoubtman2 years ago
BC 548 is used to amplify the sound if you don't use it, the sound will be low
vishalapr3 years ago
This is so cool and cheap!Just the kind of project I like!
Have a look at my ibles!!!