Quiet, 24VDC Motion Detector?

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Hi All,

I haven't lurked around here for a while, but I now have a question
that I think this group can help me with, so without further delay...

Any suggestions for a motion detector that is
a) Inexpensive,
b) Operates on 24 Volts DC
c) Is silent/very quiet?

This would be used for detecting activity in a room (and due to the
geometry of the room, I'll be using at least 3, which is why "the
cheaper the better" is becomming my mantre here). I don't need pet
imunity, I don't need tamper contacts, I don't need a walk test LED.

Straight PIR is fine by me, and I don't need microwave. Contacts can be
normally open or normally closed.

If there isn't such a thing as a "Cheap, quiet 24 volt motion detector"
I could make a "Cheap quiet 12 volt motion detector" work, but that
would mean adding additional power supplies which I'd like to avoid.
Large emphasis on QUIET. I used a old(er) FBII PIR for my
proof-of-concept and -- this may sound wacky, but -- the sound of the
relay clicking on and off drove me batty.

Bonus points if it can be purchased at retail in the Cleveland, Ohio
area.

Thanks,

Lincoln