detecting presence inside - PIR or ultrasound?
PIR sensors work fine and are probably easier to program for than ultrasonic sensors. For example, this tutorial on a PIR sensor sold by Adafruit has a datasheet at the bottom that says:

Operating Conditions Operating Temperature -20 ˚C to +70 ˚C
Storage Temperature -30 ˚C to +80 ˚C
Operating Voltage 3 to 10 V at Rs = 47 kΩ

You can try to find and check the datasheet for the sensor you intend to purchase to determine if it will work.