Another, more permanent, repair for an old doorbell circuit is to use a small ac adapter in place of the battery. Most people will have an AC adapter left after an old radio or similar device has long since died. Look for an output of 10 to 16 volts printed on the side of the adapter casing. Current ratings will typically be very low from these adapters, around 500mA, making them perfect to power the doorbell circuit. All that is needed is a conveniently located receptacle to plug the adapter in.
This drawing illustrates the wiring for a split receptacle controlled by a switch. The tab connecting the hot terminals on the receptacle is removed and the source hot is connected to the bottom half. The source neutral is connected to one of the neutral terminals on the receptacle.
This type of switch will be referred to as a 2 circuit lamp switch when shopping at home stores. Don’t mistake this for a three way switch (pictured below), the two do not function in the same way.
With this lamp, bulb A can be turned off and on independently and switch B can turn on bulb 1 alone, bulbs 2 and 3 together with bulb 1 off, bulbs 1, 2 and 3 all on at the same time or all three off.