I am 73 and need to monitor my heart rate per my cardiologist. I do High Intensity training at a local facility 3-4 days a week and I also go to YouFit and lift weights. I have been told to keep my heart rate at 95% of my max or lower.
The High Intensity facility uses HR monitors and that show what you are doing on a screen. The problem is what their HR monitor shows is often 150%+ of my max. I know my HR is not at 150% my cardiologist agrees he said if I was actually doing that I would have dropped a long time ago.

I'd like one that would record to my iPhone.

Anyone use one they like?

This is what I have. When I bought it, it was only $35 so I don't know WTF happened there.

The main thing to look for is that it monitors with a chest strap. The finger ones are worthless.

More expensive monitors will also record and track your HR through the whole session that you can upload to your computer. Don't know anything about phone aps for them.

The chest straps usually are interchangeable. For example, I could use just the chest strap with a piece of cardio equipment like a dreadmill without needing the watch part (as long as the machine has a built in HRM).

I'm using a Sync hrm (mountain biking). I've got about 100 hours on it and it seems to be doing what it's supposed to nice and consistently. It works with my phone through Bluetooth, and is compatible with most of the standard apps.  Oh and it was about $18.

#1....

Make sure your doctor tells you what your MAX heart rate is, or what the BPM is at your 95% ceiling.

#2....

Don't pay any attention to the %BPM numbers (like the 150% reading the machines were telling you). See if they
will actually tell you the realtime BPM and use that to compare to #1 above.

I say this b/c most machines will ask you your age. They calculate your Max. BPM based off your age
(some number - your age = Max BPM). I forgot what the number was, but you can google it. Basically,
your real Max. BPM may be much higher than the machine calculated Max BPM. That's why you should
ask your doctor what that number is.

-ZA

I've been using the Armour39 from under armour. I bought it at the UA outlet for $30(for the chest strap). So far so good. Been on a few runs with it And have had no issues. You can buy a watch that goes with it or it just connects to your iphone using the armour39 app via Bluetooth and saves your workouts.

Here are some screenshots of a completed workout.








There are a lot of places still selling this for $100... If you look around online you can find them for $30 or if you have a UA store around. The reviews that I've read were mostly complaining about how it's not compatible with android devices... Luckily... I use an iPhone

Garmin Vivofit.  It's an electronic watch that costs about $80.  Here's a review.

Then, you need a chest or wrist strap.  Here's a Garmin one for $34 that I've personally used.  It works well and gives an accurate reading.  It looks like it would be uncomfortable to wear a chest strap under your shirt, but it is comfortable and you forget you're wearing it.  If you prefer to wear a wrist strap instead of a chest strap, there are several options.  The Mio Link wrist strap is one.  I like the chest straps.

The strap measures your heart rate and transmits it wireless to the watch, which displays it.  It is very easy to use and works well.  The watch has other functions if you want to use them, or else just use the HR monitor which is what I do.

eta:  My advice is to stay away from cheap-o units.  You will find offbrand HR monitors for at a good discount.  They may work for a little while, but they're usually crap and will stop working or will just be a pain to use on a regular basis.   Been there, done that, have a door weight HR monitor as a souvenir.  Garmin is a good brand, and the basic models like the Vivofit get great reviews.

How do you know what your max HR is?