Here's a Python function I've written for that purpose:
def str2bin(msg): return ''.join(bin(int(i.encode("hex"), 16))[2:] for i in msg)
There's probably a better way but this works for me.
The function makes us of a generator expression to encode each individual character in the original string into it's hexadecimal representation and using bin to turn that into a binary string. The leading 0b is stripped off before they're all combined back together into a single string again.
Useful if you want a long string of bits to play with.