AS checks on auction status at varying intervals, depending on how much time is left in a given auction. If there are more than 3 days left, AS may not check your bid against the current high bid on the item at all. Then as time winds down in the auction AS checks your bid against the current high bid more frequently. If at any time a comparison reveals that your max bid has been topped by a current high bid, AS notifies you to that effect. Thus, outbid notices are far more likely to be sent when the time in the auction is short and AS is comparing more frequently. AS still may not catch an outbid situation, but it's more likely that it will. I just had one such notice waiting for me this morning; it said there were "20 hours, 31 mins +" left in the auction at the time the outbid notice was sent. I cancelled my snipe, but the warning came with plenty of time to increase my max bid if I had been so inclined.