It should still be good, I have seen some left out for a few days and had no problems. Now dont quote me on this but I heard if you squirt a little on your hand and smell it and it is still a pretty potent smell it should be good. Like I said I dont know if it works or not. Another thing you can do is take a few ius and wait to see the first signs of hypo, obviously have 50-75g of quick carbs (sugar soda or juice) on hand to pound at the first sign. Be very carful if you do thid though!