The self service machines have enough trouble scanning barcodes in the clubcard app - or responding in a timely fashion to an item being scanned. The "Activity" light which I assume to the be HDD light is flashing away like a disco light at a rave, and often when it speaks the sound is choppy.
The Tesco self service machines also behave like tech support on the phone - they don't like you jumping ahead when you already know what it is you want to do. For instance, my Tesco won't let me enter my PIN number in until it has told me to, but it's still spieling out the ways I can pay - while I have already selected to pay by card, and been told to put my card into the machine (on screen) and the little light on the card reader has turned on, I have already said I don't want cashback - but the voice hasn't even reached the part where it says "sssselecccct ccccaasshhhbaaack amounnnnnnt"
ASDA used to be the same but they upgraded their machines recently - and the voice actually gets stopped if it is still speaking at each step. So my checkout process goes something like "beep, beep, beep, unexpect.... beep, beep, beep, beep, beep, blah blah blah notes are dispensed below the scanner, please insert you..... select cashback am..... please enter y..... Thank you, please take your shopping.....<10 seconds later> Please take your shopping"