Motion sensor to signal a PC?

[DeanB <deanbrown3d@xxxxxxxxx>]

Hello,

I want to link a motion sensor in my house to a PC, so that I can
write a program to email me if there is activity. Is there such a
thing? I understand that some network cameras have similar functions
(for example FTP'ing file on motion sensing, or sending emails
themselves), and I have played with them in the past, but is there a
simple motion sensor equivalent?

Thanks!

-Dean