Many other potential variables as well. When experiencing this event, how long does it take your heart rate to reach a point it can be identified as worthy of triggering the switch? Is the laptop still in range of your smart watch at that point? Then there's the reliability of the wireless connection and the watches ability to accurately read your heart rate (make sure it's seated correctly).
If this is a situation you're actually concerned about, the approach in the article seems simpler and more foolproof.