The controversy on the second day follows Alex Carey being given not out on Wednesday, when England reviewed a caught-behind decision with the Australia wicketkeeper on 72.
He was given not out because the spike which appeared on the technology was out of sync with the pictures, but that was later revealed to have been an error by the operator.
The first incident on day two occurred in the 44th over, with England 149-5.
Australia appealed for a catch after a ball to Smith looped to Usman Khawaja at slip and the on-field umpire Nitin Menon sent the decision to the TV umpire to check if the ball had carried.
TV umpire Chris Gaffaney then deliberated over various replays, first checking whether the ball had hit Smith’s glove or helmet.
While the TV pictures seemed to suggest the ball must have hit glove, the Snicko technology seemed inconclusive – the spike was as the ball passed helmet not glove – and Gaffaney deemed the ball had hit Smith’s head.
The hosts’ fielders were visibly disgruntled and one Australian was heard saying “Snicko needs to be sacked” over the stump microphone.
Marnus Labuschagne added: “Nitin, this is outrageous.
“Has the ball gone through his glove?”
Menon was heard explaining: “We checked for fair catch because we felt it was off the glove but he says it is off the helmet.”
In any case it appeared the ball did not carry to Khawaja.
The second decision ultimately resulted in Smith’s dismissal.
He attempted a pull shot to Pat Cummins but Australia appealed confidently for a thin edge.
Smith appeared certain he had not hit the ball and was ready to review the decision had it been given out on the field.
Again umpire Menon suggested he was not sure if the ball had carried so sent the decision for Gaffaney to review.
As the players came together to await the decision, Nathan Lyon was heard asking non-striking batter Ben Stokes if he heard anything.
Gaffaney said “there is nothing obvious there” after viewing an initial replay but Snicko showed a rough spike within a frame of the ball passing the toe of Smith’s bat – the leeway allowed in such scenarios.
Smith was given out. Both he and Stokes seemed frustrated with the decision.
