The app should come with your hardware...

I stopped buying straps because they didn't last much, I'm happy with an electronic watch that does all these kind of things and more, I'm trying to record my activities, then I can look at all these stats, HR zones, etc, but mostly average and max HR.

Some watches connect to bike computers too, so you can monitor HR in real time!

On a different note, remember that if you go above zone 2, it takes 20-30 minutes for your metabolism to come back to fat burning, so even detailed HR/power stats won't tell the whole story...