What does 5 ATM mean?
It survives static pressure equal to 50 m of water. Fine for swimming, showers and rain — but not diving, since diving adds dynamic pressure spikes that exceed the static rating.
A $59.99 band with no screen still packs a dedicated ECG chip, a skin-contact thermistor, a MEMS accelerometer, Bluetooth 5.3, 5 ATM water resistance and magnetic charging. Here is what every one of those specs actually does. Drag the exploded stack to rotate it, then tap a layer to jump to its explanation.
This diagram renders with SVG so it works on every device, with or without WebGL. Drag left or right to spin the stack.
Every heartbeat starts with a tiny electrical pulse. An ECG (electrocardiogram) sensor measures that voltage directly through two metal electrodes touching your skin, producing the classic PQRST waveform below. Optical PPG sensors (the green LEDs on most watches) only watch blood volume changes in your skin, so they infer heart rate indirectly. A single-lead ECG is more direct and can even hint at rhythm irregularities, which is why a dedicated ECG chip in a $60 band is notable.
Slide the rate and watch the beats pack closer together. At 40 BPM (resting athlete) beats are 1.5 s apart; at 180 BPM (sprint) only 0.33 s.
An NTC (negative temperature coefficient) thermistor is a resistor whose resistance falls as it warms up. Press it against skin, measure its resistance, and you get body temperature with no moving parts. The steep curve around normal skin temperature is exactly why NTCs are chosen: a small temperature change causes a large, easy-to-measure resistance change. Drag the handle along the curve.
A MEMS accelerometer is a microscopic silicon mass on springs. When you move, the mass lags behind and tiny capacitance changes reveal acceleration along X, Y and Z. Drag the chip below to tilt it and watch gravity redistribute across the three axes. Steps are detected by counting rhythmic peaks in the combined signal.
It survives static pressure equal to 50 m of water. Fine for swimming, showers and rain — but not diving, since diving adds dynamic pressure spikes that exceed the static rating.
Lower power draw for longer battery life, and better coexistence: it hops around Wi-Fi and other 2.4 GHz traffic more intelligently, so syncing stays reliable in crowded radio environments.
No exposed port means no water ingress point and no corroding pins. Magnets self-align the contacts, which is why nearly all sealed wearables charge this way.
Five quick questions on what you just learned. Instant feedback on every answer.