nowadays, even i use my DA to purchase online at 1am for only RM34.xx (after convert), they will immediately call me to verify.
maybe bcoz online transaction, and at midnight.
same goes to HSBC, i swipe rm9k 1 shot and they immediately call me to verify too.
but if swipe 2k, 3k, they never call
even DA, previously i swipe (err, slot, actually?) my card twice at esso pump, they immediately blocked the card.
usually bcoz of smiles card cant be read (esso, credit card 1st then smiles card. shell, bonuslink 1st then credit card).
so at esso credit card already authorized, but smiles card cant read, so i cancel it.
when i swipe (slot) the DA card for 2nd time, declined!
i immediately call the bank and they told the card had been blocked (afraid for unauthorized use for petrol).
i verify it and ask them to unblocked it.
this happen to me 2x in a same day! i pump once at morning and again at night.
solution: redeem points till finish and apply new smiles card
(my 'damage' smiles card cant be read at petrol pump but no problem if swipe at cashier inside

)
this story happen b4 pbb offer esso/mobil

I notice they will monitor on your spending habit, for 1st time spending on internet transaction and huge amount, normally they will call and verify
it happen to my mum when she took Citibank CC to buy plane ticket, immediately called up and verify
2nd time swipe in Thailand, didn't inform Citibank prior that and bought some jewelry and they immediately called up as well, lucky my mum phone was on that time
Maybank? didn't call up to verify at all and my parent had been using for around 20 yrs