Transiently-powered devices are a class of small devices powered by energy harvesting. Because such devices are subject to frequent power outages, many recent works propose to checkpoint data residing in volatile RAM into non-volatile RAM. In this article, we propose a new incremental checkpointing mechanism supported by a common hardware component, namely a Memory Protection Unit (MPU). This mechanism leverages the hardware interrupts of the MPU: volatile RAM is read-only on boot and is progressively unlocked as soon as protection violations occur. The MPU interrupt handler is designed to flag the corresponding volatile RAM blocks as dirty, i.e., modified. When a power outage is foreseen to be imminent, the software simply has to copy the dirty blocks from volatile RAM into the non-volatile RAM to ensure application progress over power outages. We validate our approach analytically and in cycle-accurate simulation, and we show that the proposed solution can be easily implemented on real hardware.