The datasheet says −20 °C to +40 °C. The afternoon surface temperature of a steel gate in Lagos or Ho Chi Minh City is 60 °C. That gap is where most field failures come from, and it is not the fingerprint sensor.
What fails first
The lithium cell. A 4200 mAh Li-ion pack loses capacity above 45 °C and degrades permanently above 55 °C. A lock that lives on a west-facing door is being cooked every afternoon, and the symptom is not “battery dead” — it is “the lock forgets its Wi-Fi and the clock drifts”.
The display. An OLED front panel rated to 60 °C is at its limit only if the ambient is 35 °C and the sun is not on the door. Behind glass, in direct sun, surface temperature passes that easily, and the first sign is a dim or ghosted screen.
The adhesive and gaskets. IMD panels are bonded; a hot-cold cycle repeated for two years lets moisture in, and then the touch keys become unreliable.
What we changed
- Face platforms published honestly at −20 °C to +40 °C, not at the chip figure
- AA-cell platforms (F32M1, F2 Slim, GA05) for exposed doors — no lithium to cook
- GA05 rated −25 °C to +85 °C because it has no display and no Li-ion pack
- Salt-spray and humidity testing documented before a model is released
How to choose for a hot market
If the door is exposed to afternoon sun, use an AA-powered fingerprint model for the gate and keep the face model for a shaded or interior door. Ask for the whole-lock temperature report, not the silicon rating — and be suspicious of any number that exactly matches the chip.