As a commuter in Sydney you've no doubt seen all the posters reminding you to tap on and off every time with your Opal card. Of course this is needed to ensure you're charged the correct fare but also to notch up your journey count netting you free travel.
Due to some teething problems it would appear that some Opal card readers aren't correctly registering taps leading to commuters being charged default fares. These charges can start to add up quite significantly and unless you're keeping an eye on every transaction you could easily miss out on a few dollars.
Although the application I develop, My Opal, isn't endorsed by TfNSW/Opal I try and do everything I can to make using Opal just that little bit easier. Now with v1.3 of the iOS app, released on Friday 05 September, it'll keep an eye out for any transactions that don't have a tap on/off over the last 7 days. Transactions are given a 24 hour "cooling off period" to allow them to complete before you're notified.
Armed with this information you can lodge a query with the Opal team to get it looked into and hopefully receive a refund. I'd love to hear from you if this feature has saved you some money!