I purchased a third party case with the magnetic sensor trip, but it doesn't work. I also found at least one third party...

I can tell you that the Apple Smart cover will put the iPad to sleep and wake it as it did with the iPad 2. 3rd party cases, however, seem to have lost that ability. My sister and I both pre-ordered iPads, she ordered the smart cover with hers, I ordered a case from Amazon that claimed to have the sleep/wake function. Hers worked, mine didn't. I'm confused.