The hardest part for this circuit was the title. It is quite easy to miss the sound of a doorbell if you are watching TV , this circuit gets round the problem by providing a visual indication, i.e. a lamp. As an alternative, a LED could also be used. You could just parallel a lamp across the doorbell, but this would mean extra drain from the doorbell batteries or transformer. Using a series resistor R1 actually reduces current flow , and if run from batteries, will give them a longer life.  The value of R1 is chosen so that about 0.6 to 0.7 volts is dropped across it, and the doorbell should still ring. I used a сombination of a 22 ohm resistor in parallel with a 50 ohm. The doorbell still rang and circuit operated correctly.