A communication system and an IoT system are provided. The IoT system is applicable to a wireless network system including an access point. The IoT system includes a WiFi module and a GPIO device. The WiFi module is configured to connect to the access point. The GPIO device is configured to provide a plurality of wake-up signals to the WiFi module through a GPIO pin. A predetermined time period between any two of wake-up signals is greater than an interval between two delivery traffic indication messages from the access point. The WiFi module includes a timer and a power management unit, the power management unit drains power to transfer the WiFi module from a sleep mode to a normal mode after the timer receives the wake-up signal.