Following the datasheet of the PIR325 the powwer supply is 2.5V to 15V, so it should run at 3.3V.
The board, as you know, is 5V only out of the regulator. But looking
at all the external circuits on the board looks like 3V would be OK, however
you would have to worst case design for dynamic range, headroom,
etc,. at 3 V to see if 3V operation feasable, or change circuit scaling and
approach to meet 3V.
Clearly PSOC can run at 3V as well, reduced clock rates for some devices.
Thanks for the fast replies, is working fine with 3 V.