The kidnappers can easily ask him to check his bank balance using the ussd Code since it's a small phone and through that means they can still know how much their victim is worth.
With the way things are going in this country we need to be wise in order to out smart our enemies. With the high level of inflation in the country, I store my money that I don't want to use and invest in Bitcoin or any other investment in usdt inside my wallet and I keep my wallet key very safe. Whenever I need money I go to p2p and sell out the exact money that I need within the week and I don't keep more than #500k in my bank account. And this alert of a thing, you can ask your bank to only send you alert on your email instead of text message. Should you need evidence of transaction you can always login to that email and see the alert in your email. We have to be very careful out there.