Even when you’re someone who gets a lot of cold calls, it is very rare to find a cold call on your answer machine.  All of the cold calling companies use computers to dial so how do the computers know the call has been answered by an answer machine rather than by a person?

The dialler computers cannot tell exactly when an answer machine answers the call but they use algorithms to make a judgement.

So, what leads the computer to think the call is answered by a machine?

1. A person tends to answer the phone with Hello then pause or something like “This is the Johnson residence, Fred speaking” then a pause. Whereas an answer machine tends to have a much longer message with no gaps then the pause.
2. They can detect the sort of background noise associated with tape based answer machines. All modern answer machines are digital – no tape, hence this method doesn’t really work anymore.
3. Listening for tones or beeps indicating an answer machine.

The dialler computer judges within a few seconds whether the call has been answered by a person and if not then it cuts the line.

These systems make mistakes and are often the cause of why you may get short silent calls.

There are rules they are supposed to follow to ensure no more than 3% of their calls end up in silent calls but whether any of them follow that rule – who knows. Some people say that if you suspect a cold call – then press the # symbol repeatedly and it will screw up the answer machine detection – but I don’t know if that’s true.

If it turns out to be someone you know calling they’ll just assume it was noise on the line and will wait for you to say Hello.