So after many hours of researching, it seems that there are three predominant methods for reading a person’s pulse:

1. LED/Photocell Finger Method: Found in local drugstores and basic hospital heart monitoring, essentially you shine a light through your finger and catch it on the other side, where fluctuations in the amount of light shone correlate with pulsing blood levels. Cheap and a relatively easy circuit to build.

2. Electrode Method: Used in ECG/EKG applications, uses electrodes attached to the body to measure the electrical activity of the beating heart. DIY circuits all come with the caveat of potential shock and death. Cheap but more complicated, potentially harmful, circuits.

3. Buy Method: Use an off-the-shelf heart rate monitor such as those sold by Polar, which come in a chest band (~$40) and wireless receiver ($14.95). The also sell an OEM board. Expensive but easy and reliable.