could I use multiple PIR sensors with a single arduino board to trigger a large speaker? I need to cover about 1 km and I was hoping to cut cost by using about 10 PIR sensors for one arduino board and about 2 boards in total. Thanks in advance. Good day
Cheap PIR sensors are only useful indoors and for distances less than about 15m.
For outdoor use the cheapest option would be to make a laser beam break sensor. Check to see if these are legal in your country and what power restrictions apply.