5 ATM water resistance
Rated for 50 meters of static water pressure. Fine for swimming, showering and rain. Not for diving, high-speed watersports or hot saunas, where pressure spikes and heat exceed the static rating.
Layer 01
The ECG chip: reading your heart's electricity
Every heartbeat is triggered by a tiny electrical pulse. A single-lead ECG measures that voltage between two metal electrodes: one on the back of the band touching your wrist, one on the rim you touch with a finger, closing the circuit across your heart.
That is different from optical PPG, which shines green light into skin and watches blood volume change. PPG estimates rate; ECG records the actual electrical waveform, the P wave, the sharp QRS spike and the T wave, which is why ECG can hint at rhythm irregularities PPG smooths over.
Layer 02
The NTC thermistor: temperature from resistance
At 34.0 °C the thermistor reads 6.7 kΩ
NTC means negative temperature coefficient: as your skin warms, the thermistor's resistance drops, steeply and predictably. The tracker pushes a tiny current through it and converts the voltage to temperature.
Because the curve is steepest right in the human skin range, a contact NTC pad resolves tiny fractions of a degree, useful for sleep staging, cycle tracking and spotting fevers, all with almost zero battery cost. Drag the handle or use the slider to see the curve respond.
Layer 03
The MEMS accelerometer: motion into math
Drag to tilt the chip. The bars show gravity split across the three sensing axes.
Inside the accelerometer is a microscopic silicon mass on springs. When your wrist moves, the mass lags behind, changing tiny capacitances on three perpendicular axes. The chip converts those into X, Y, Z acceleration values hundreds of times a second.
Steps counted: 0
Walking makes a rhythmic bump in the signal. Firmware counts each peak that crosses a threshold with plausible timing: that is your step count.
Spec decoder
What the rest of the spec sheet really means
Bluetooth 5.3
Lower-power connection subrating and better channel management mean longer battery life and fewer dropouts when your wrist shares airspace with Wi-Fi, earbuds and dozens of other radios.
Magnetic charging
Two spring pins snap onto pads via magnets. No fragile port to seal against water, so the case stays fully closed, which is a big part of how a cheap band earns a 5 ATM rating.
Check yourself