Checking for a bit pattern

A bit array will take an array of bytes in the constructor, so you can just pass in the byte array.  Alan's solution may be a little easier though.  It doesn't seem that Microsoft provides a method to take a piece of the BitArray. CopyTo is the closest thing, at this copies the entire array at a specific index.

BitArray mainarray = new BitArray(myBytes);

Theoretically their may be a way to do the comparison by sliding a BitArray with your pattern along the big bitarray record and the Xor  method of the BitArray ,  also masking the other bits in the main array with 0000s (using the And method of the BitArray).  Then use CopyTo to copy the entire contents to a boolean array, and essentially search for a single true boolean value.

If you don't mind using strings for this, then the following approach should work. I've just used a 5 byte array for illustration and, as expected, the pattern is found at bit 17 (zero based):

using System;
using System.Text;

class Program
{
     static void Main()
     {
          byte[] ba = new byte[5]{1, 2, 39, 4, 5};
          string pattern = "0100111"; // decimal 39
          StringBuilder sb = new StringBuilder(8 * ba.Length);         
          int temp = 0;
          foreach (byte b in ba)
          {
             temp = int.Parse(Convert.ToString(b, 2));
             sb.Append(temp.ToString("00000000"));
          }
          string bitArray = sb.ToString();
          Console.Clear();
          Console.WriteLine("Bitarray is {0}", bitArray);
          Console.WriteLine("Pattern is {0}\n", pattern);
          int index = bitArray.IndexOf(pattern);
          if (index == -1)
              Console.WriteLine("Pattern wasn't found");
          else
              Console.WriteLine("Pattern first occurred at bit {0}", index);
          Console.ReadKey();
     }
}