Smartwatches

Roughly — research shows smartwatches typically miss actual calorie burn by 20–40%. They're reliable for comparing workouts (workout A was harder than workout B), but not precise enough to base weight-loss diets on. Use them as a consistency and intensity tool, not a calorie ledger.

Apple Watch is the best all-around smartwatch if you own an iPhone — great fitness features plus everyday utility. Garmin is the athlete's choice — superior GPS, battery life (often 7–14 days), and running/cycling metrics. Fitbit is a simpler, lower-cost fitness tracker option. For serious athletes who want detailed training data, Garmin wins; for general fitness and daily use, Apple Watch wins.

For most users, no — modern wrist heart rate monitors are accurate enough for zone training. But chest straps are significantly more accurate for high-intensity intervals, sprints, and strength training (wrist HR sensors struggle when your wrist bends or muscles flex). Serious athletes often wear both: watch for GPS and phone connectivity, chest strap for HR accuracy.

Partially — most watches detect heart rate and have a "strength" or "weight training" mode, but they can't automatically count reps, sets, or weight. Some premium watches offer manual rep logging through the app. For pure strength tracking, a dedicated app (Strong, Hevy, FitBod) paired with a smartwatch for HR is usually more useful than the watch alone.