A cellular modem is configured for low power applications. In some instances, the cellular modem includes a transceiver, a processor to control the transceiver, a memory device in communication with the processor, and a general-purpose input/output (GPIO) pin, controlled by the processor. In an example, the cellular modem receives an appointed time for an upcoming communication and determines a time to activate a power supply. The determination may be based at least in part on the appointed time for the communication, so that the power supply is ready to supply power at a level consistent with use of the transceiver at the appointed time of the communication. At the determined time, a signal from the GPIO pin is used to activate the power supply, resulting in an increase in power supplied to the cellular modem in a just-in-time manner.