The reliability of electronics products has become a serious problem due to the increasingly harsh environmental conditions when the products are in use. Due to demand on greater performance and higher integration in microelectronic devices, the electronics industry has been seeking suitable components, packaging and cooling techniques to achieve low-cost and high-reliability. This paper presents the experimental verifications to analyze the effect of temperature and humidity on the electronic circuit as well as evaluating the device reliability, using Xiaomi Band 2 as a real case. It is found that 125°C has been a critical temperature for the smart watch, above which the sealed plastic case ruptured easily. However, 150°C has been found to be the temperature to burst the battery. Cold storage test with a temperature of - 70°C shows that low-temperature will only cause the smartwatch to hibernate, even for up to 400 hours, after which the device will be restored to work under a room temperature. Humidity has been found to be a crucial factor in damaging the device, which changes the rubber ring and plastic case into brittle and corrodes the interconnects on printed circuit board. Further investigation into the microstructure evolution of interconnects has found that the highly accelerated stress test has caused serious cracks in solder joints and electronic components, such as, resistors and capacitors. In short, the smartwatch can work under harsher environment than the designated environmental conditions in the product manual.