How many weeks does baby have heartbeat??? Because I got this heartbeat monitor and hear things could it be sign of pregnency????

Doubtful. you can hear a baby's heartbeat at 20 weeks gestation with a stethoscope. The heartbeat is detectable much earlier, maybe 10 weeks or earlier with ultrasound. Your heartrat rus 60-100bpm, and a babies will be 120-140bpm. I doubt that you are hearing a baby.
6-8 weeks. That would be 6 weeks on a monitor and 8 weeks with a stethoscope.