What's a beta guy? If I were to describe such a man in a nutshell, i would call him "unsexual". That doesn't mean a beta has no sex drive, and it doesn't mean you are alpha if you have a high sex drive. Being unsexual means that you are not transporting any sexuality outside of your mental world. Alphas show openness with their body language, they show that they are comfortable with their body, they seem to show that they are sexually active. Women will notice that, they have very fine sensors for that.
But its not only body language. A beta will often be very polite, especially to women, listen to them carefully, laugh at their jokes (or act as if the jokes were funny), concede with every single of their opinions, pretend to be into girly stuff. With that he will signalize: "I do and will be every thing you want. You have complete power over me."
That's very nice and maybe a foundation for a friendship, but it doesn't signalize sexuality. Women generally have a very high emotional competence, meaning they can sense this from a hundred miles away: "This guy will do anything I say. He is worthless". Again, the terms I use may seem brutal, but they describe what I want to say very precisely.