Home fetal doppler question?

I know they don’t recommend use of them I don’t need anyone telling me that it was a personal choice I wanted. So anyways I received it today, tried for the first time I heard the heart beat! I am only 10 weeks so I know your suppose to be further along, but what does the bell warning sign on it mean? And it was saying the heart rate was like 70-80 which I know has to be wrong lol so just wondering if it’s saying that because I’m too early for it to correctly detect it? I’ll try again in a few weeks! 😁 ps I checked the manual it don’t describe what the warning sign means.