There is a color LED bulb to indicate the heat setting - green light means the warmer is working at level 1(50℃); red light means it is working at level 2(60℃)
Featuring various protections, including overheating, overcharging, overvoltage, it is safe to use.
It can supply electricity for you mobile phone as well, while it will not heat up to keep you warm for charging phone will generate heat and it is dangerous to heat up from during charging period.
Rounded smooth housing feels very comfortable in hands and is less likely to be scratched in daily use.