Which motion sensor would I use?

Which motion sensor would I use in the following situations?

To detect when someone is walking in a room. Would the applicable sensor to use be a PIR Motion Sensor?

To detect when my physical mailbox is opening up. I'm not sure what sensor I would use for this?

Also if I wanted to email the results to myself, I would use a WiFi shield?

I didn't know there was over 100 components for this. Jeez. http://playground.arduino.cc/Main/InterfacingWithHardware#motion_gyro

Any help and I'd appreciate it. I'll start with the door project first because it's more novice.

For person walking into room, your choices are

PIR motion sensor. detects warm people. only works if room is cold, and not zombie. Some kind of beam interruption sensor in the doorway. Radar. Ultrasound.

For mailbox:

Some kind of reed switch or hall effect sensor, triggered by the movement of a magnet glued onto the mailbox door.

Problem with PIR is that yes it will trigger when the person enters the room and disrupts the heat pattern, but if the person then stays still for a few minutes, the PIR will adjust to that new pattern and alarm when the person moves again.

Wow! Thanks!

I was thinking maybe a light sensor too. Since the mailbox is dark and when its opened up light comes in. I bought a PIR sensor. I’m debating on a radar sensor but I might still be too noob for that.

Also is this a standalone shield? It’s like an Arduino Uno + wifi Shield combined?