Another is an , which acts like a thermometer, translating the "heat" of the room into a number the Watchman can understand.

Sometimes, the Watchman needs to move a huge pile of logs (data) from the thermometer to a storage logbook. If he did this himself, he couldn't watch the door. So, he uses his assistant, the Direct Memory Access (DMA) controller. He tells the DMA, "Move these 100 readings to memory and let me know when you're done." The Watchman stays focused on the big picture while the data moves in the background.

Most of the time, the Watchman is in a "Low Power Mode," dozing lightly to save energy (essential if he’s running on a battery). Suddenly, someone forces the greenhouse door open.In a normal computer, the CPU might be too busy to notice. But the Cortex-M has a Nested Vectored Interrupt Controller (NVIC) . This is like a red phone on the desk that rings instantly. The Watchman drops everything, jumps to the "Door Emergency" page of his manual, sounds the alarm, and then returns exactly to where he left off.