I have been using the clearblue digital OPT and I have been on high fertitility with the flashing smiley for 3 days now, testing with FMU and again around 5pm. I had to buy a new pack because I ran out of test strips. So I thought for the heck of it to test my old one with the new one. I still got the flashing smiley with the old one but the blank circle with the new one. Tested both in the morning and again at 5pm.