Play sound through tablet/mobile device when card transaction approved/declined

[#1]

My store serves a lot of elderly customers who are hard of hearing and they prefer an audio feedback to confirm that their card transaction was approved or declined.  They often don't even look at the mobile device screen to confirm their transactions are approved or hand it back to me after they tap their cards (which is a bit frustrating, but I try not to correct them on it).  As the Reader will sometimes beep when a card is tapped and then requests that the card be inserted or will beep before finding out the card is declined, the noise from the Reader also generates some false positives that I would like to eliminate with an alternative audio feedback.
Since my mobile device has nice loud speakers and can do more than a single-tone beep, would it be possible to add the option for 2 different audio cues that play from the mobile device or tablet when a card transaction is approved or declined?