Smart ones no need to check. Take note:
For all MRT stations- if u r using adult fare cards, the moment u
tap on the fare gates, a blue ( some green ) light will flash on
the LED blinker. However if u r using children/senior
citizens/concession cards like me, you'll not see blue light but a
yellow ones.
For all buses- if using adult cards, the moment u tap, u'll hear a
single beep tone. However if u using children/senior
citizens/concession cards, you'll hear double beep tone.
No need to ask passengers take out cards to check! Simply by
listening can already 
