In a previous article, I was proposing a sketch for an alarm using a movement detector. As I plan to design a full alarm with several devices, I tested it. Conclusion : powering it with a 9V battery 200mAH, it only lasted for 12 hours. Not enough for an alarm designed to last at least 1 month (aim I chose).
Indeed the energy consumption of of the Arduino board (Uno or Nano or whichever) is quite high. I advise to read this article that explains that in detail.Now should be around 35mA. I’ll keep posted with the result as I’m experimenting the sketch writing those lines.