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I think you are talking about PIC16 F 84A microcontroller.
by the way you can't program it using C++. you van only write its code in assembler or C. if you decide to use assembler you need to download free microchip development tools. If you choose C you need a C compiler like PICC or CCSC. they're not free unfortunately. those compilers contains an help menu with all functions.
I use CCSC. it's almost like standard ANSI C.
schematic for your alarm depends on sensors you decide to use.