Wifi RFID reader with battery power supply


I'm a complete arduino & electronics noob but know how to program.

I want to create a home security system. I want to put an RFID reader inside my front door. Family members will swipe a card/fob when they go into the house, and if everyone is out at the same time it will put my webcams into alert mode to alert us about movement. There's no mains power just inside my door so I want this to be battery powered.

I was thinking of using a Mifare RC522 Card Reader with an Arduino micro or nano (I want the lowest powered one) and the wifi shield, and powering all of this with a battery. It'd communicate with a control computer on my home network over HTTPS.

My questions are:

  1. Could I run this device from a 9V battery?
  2. If so, how long would it be likely to last (I don't want to have to change it every week).
  3. Are the arduino micro & nano compatible with the wifi shield (and how would I know? The wifi shield docs don't list compatible boards)?
  4. Would a 433Mhz RF transmitter be more power efficient? If so, I might use one of those instead.



What about an RF transmitter instead? Wouldn't that be a lot more power efficient?

The simple 433 MHz transmitters should work well and are low power. However, an RFID card reader is power hungry and has to be active all the time, or activated at very frequent intervals, so to estimate battery life you need to know its power requirements. A passive magnetic strip card reader would consume far less power.

OK thanks, I'll look into a magnetic reader, or maybe put a button on the device to power the RFID reader so it's not always powered on.