A glass-tube heater includes a glass tube, a cap, and a temperature display unit. The glass tube is provided therein with an off-water protection sensor or a tipping switch, a control circuit board, one of a TRIAC and a relay, and a heating element. The control circuit board includes a control unit (which is an MCU or a comparator). All the components that are disposed in the glass tube are electrically connected to form a control circuit. Devices for temperature control, detection, and heating are all disposed inside the glass tube. The off-water protection sensor is operable to detect if being removed out of water for controlling the heating element to carry out heating or not, thereby ensuring quick termination of heating upon removal out of water. The tipping switch is operable to control the heating element from heating in case of excessive tipping of the heater.