Polar no longer makes the M400. We reviewed a deep field of well-designed devices. As smartwatches merge with GPS watches and then absorb activity
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Polar M400 review: A feature-packed GPS running watch that can also track your steps and sleep - CNET
Polar M400 GPS & Activity Tracker Watch In-Depth Review
Polar M400 GPS & Activity Tracker Watch In-Depth Review
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Polar M400 review: A feature-packed GPS running watch that can also track your steps and sleep - CNET