PIR Motion Sensor + ATTiny85

I'm making a project where i use a PIR motion detector and a ATTiny85 chip. The only problem is that ATTiny85 runs at 3 volts (2XAA), and the motion sensor needs at least 5 volts. What is the best way for using just 1 battery, or can it also just run on 5 volts?

Sensor: http://vi.ebaydesc.nl/ws/eBayISAPI.dll?ViewItemDescV4&sd=3&item=111048574246&bv=safari&t=0&nv=2&js=-1&ssid=15&category=42889&ds=0&seller=eshop2098&caz.html