Reducing power consumption of mailbox alert

I want to build a mailbox alerting mechanism. It will consist of 3 parts.

  1. Mail drop detection
  2. Mail retrieval detection
  3. Wireless communication to our house.

Since this will run of a 9V battery I want power consumption to be as low as possible.

As for wireless communication, I found a module which has a 32uA sleep mode. Since it only needs to communicate when an event occurs, it could be sleeping most of the time.

As for mail retrieval I though of using a nc/no push button, which activates only when the door is opened. This would mean no current is flowing at all as long as the door is closed. I am unsure if this button will fit into the mailbox though, as i may not cut parts out. What other ideas do you have for this?

My biggest problem is the mail drop detection. I was thinking of this flex sensor. Flex Sensor 2.2" - SEN-10264 - SparkFun Electronics
But would this even sense very light mail dropping through the slot in the top of the mailbox? And how long could I expect my battery to work, when this consumes 0.5 watts?
I don't want to use a light sensor as other people might open the drop slot for no reason. The sensor here should actually detect mail being dropped in.

Thanks for your ideas.

Since this will run of a 9V battery I want power consumption to be as low as possible.

You’re already losing more power in the regulator than you’ll save by putting the processor to sleep.

Just read up on voltage regulators. I was unaware that they dissipate the extra power through heat. So I'll have to go with 4.5V directly connected to my circuit. Thanks