A warmer device includes a rechargeable warmer bag containing liquid, a protection device for disposing the rechargeable warmer bag thereat, a charging unit for charging the rechargeable warmer bag to heat up liquid at a usable temperature, and a monitoring device for monitoring the rechargeable warmer bag, wherein the monitoring device includes an actuator operatively linked to the charging device and arranged in such a manner that the actuator is switched on to ensure the heating unit being operated to heat up the liquid, wherein the actuator is actuated by the bag when the bag is expanded, such that the actuator is switched off in response to an expansion of the bag at the protection device to cut off a power supply of the charging unit for preventing the bag being over-expanded.
