Another giveaway is an extra pause before they start talking. This is call software that lets them dial a bunch of numbers at once until someone answers and it switches the person that answered over to an available headset.
If you answer and say hello and there's an extra second just hang up. They'll call back if it is important.
There’s also a very distinct “bloop” sound from their phone system, I assume it’s the sound of “connecting” you to their conference. Honestly, that is a 100% signal of a scam call that would be trivial to detect en masse in an automated system.
If you answer and say hello and there's an extra second just hang up. They'll call back if it is important.