Subject: how to detect heart rate

Hi! Thanks a lot for the response to my previous query about heart rate 
measurement. Actually, what I meant to ask was what other methods are there 
for measuring heart rate apart from using ECG. the existing query (How does an 
electronic heart rate monitor work?) on madsci 
that I read through was focussing mostly on ECG. However, I'm interested to 
know if there are other methods available for detecting and calculating heart 
rate with an electronic device.

Hope that this is clearer than my previous query?

Thanks once again! :D

Re: how to detect heart rate