You'd use something like $bv = pack('B*', $byte); to turn your string into a bit vector. You can use vec to access individual elements.

If you were to do that, it might simplify your code somewhat. The first regex could be replaced with:

if ((vec($bv, 0, 1) == 1) and (vec($bv, 4, 1) == 0)) {
    # do something 
}
[download]

I'd probably turn your string into an integer and use bitwise operations to work on it.

Update: After studying this a bit more, it'll take more work to use vec to replace the regex. Use logical and, not, or, and xor as tye suggests. The bit-shifting operands will also come in handy.