If you want to keep track of your workout, a sport watch is a great choice. The built-in heart rate monitor helps you keep track of your heart rate.
From OnBuy
Garmin vivomove 3S Hybrid Smartwatch (39mm, Silver Stainless Steel Bezel/Granite Blue Case, Silicone Band)
Gadcet
vívomove® 3S Silver stainless steel bezel with granite blue case and silicone band, New