Are PIR's always this sensitive?

[not_real@xxxxxxx (Beachcomber)]

I installed an inexpensive, battery powered X10 PIR outside my front
door, initially thinking that if I kept it out of direct sunlight, it
would function reliably.

The problem was that it was super-sensitive and would trip as cars
drove by on the street 100 ft away, and often for no reason at all.

So I relocated the unit to face down from the entry overhang.   The
false alarms were reduced but not eliminated.   I would get a trip
about once or twice a day at totally random times.

Question - Is it typical for a single PIR unit to spontaneously trip
like that?   Is that why they have dual PIR units?

What would be a reliable outoor model that could pre-anounce visitors
without false tripping?  It does not have to be tied into the main
alarm system.

Beachcomber