Get notified of incoming Bitcoin transaction, as soon as it broadcasted
If using the wallet notify option in bitcoin.conf, you can get a notification any time a transaction occurs on the network that matches a bitcoin address in the wallet. To use this, of course, you'll have to keep Bitcoin-QT or bitcoind running at all times.

https://en.bitcoin.it/wiki/Running_Bitcoin

Once you have the transaction id, you'll have to look up the transaction, either at an online service like blockchain.io or use a bitcoind json-rpc command to learn more about the transaction and what action you would like to take.