FIRST ALERTDual Sensor Smoke and Fire Alarm, SA3210, White

I recently purchased three of these smoke alarms from Amazon. Can you tell me how high up on the wall the alarm should be installed as I do not want to install on ceiling. I specifically purchased these as they can be ceiling or wall mounted. Thanks.

Is this detector a photoelectric or ionization type?

Does the unit beep to tell you that the battery is running low?

5 or 10 year warranty? Picture & Description say 10, Features says 5.