Haven't properly set off the alarm, but the lock is well built and looks like a decent deterrent to prospective thieves. I'm storing my bike in a open shed secured to some rails and all I needed was that extra safety of an extra alarm...
I use these for the sliding windows of our garden shed, and they add that bit more safety to it, so it's a bit harder to break in. Whether this is enough for your patio door is for you to judge, but the product itself does the job and works just fine, it just doesn't look unbreakable but you wouldn't expect that from a lock that costs less then £10 for a pair, would you...
IKO Super Shed Felt | Black 8m x 1m | Garden Roofing Felt Bitumen Roof Sheet