If you are really serious about about about improving your fitness. A Heart-rate Monitor could be as simple as keeping track of your exercise zones. Each zone improves different areas of fitness. The moderate zone of 70 to 80% improves you aerobic fitness.
Currently there are some excellent heart-rate monitors and not just the Polar brand. They are more comfortable to wear and easier to download your results. The weight loss is not the only important gains at 60 to 70% of your maximum heart rate but improved fitness could help you live a healthy lifestyle and may even increase your lifespan.
The new heart-rate monitors now come with the ability to adjust the zones according to the person physiology and adapted as the person gains fitness.
It is very important before attempting any exercise to go and see a medical practitioner.
I will road test a heart-rate monitor soon to see what benefits I gain from it.