The strap will only detect one person's heart rate at a time. So yes, two or more people can have a single strap paired to their devices. However, if the users are close together the heart rate from one could be recorded on both.
FYI anyone trying this, be warned - I just paired my partners HRM-Pro with my phone and it's stuffed up my step data, adding his steps while wearing it to my daily step count for every run he's used it on :-/
