"alerting him" is a perfectly acceptable and usable part of a sentence in written English.
For example, "The teacher caught the student texting in class and quickly alerted him to stop."
Manning often sends texts messages to Reich, alerting him to plays he thinks are useful.
Soon, writers were leaving messages on his studio phone alerting him to new pieces.
An aide handed Schaeffer a note alerting him to the breach.
The buzzer alerting him to voting time on the House floor blared intermittently.
During World War I it became tactically desirable to bombard an enemy position without alerting him by ranging shots.
The impetus was a call from Larry Gagosian, the Manhattan dealer, alerting him to Mr. Saatchi's intention to sell.
Whenever the bullpen phone rang, alerting him to warm up, McGraw appeared to be the essence of energy.
Two and a half months after Christopher's death, Stephen Torres wrote to Mayor Berry, alerting him that another unarmed man had just been killed by police.
He described getting a call on the morning Mr. Smith's op-ed article was published, alerting him to the scathing critique of life at the firm.
Alejos had received a call from a friend alerting him that something surreal had just happened at the funeral — something with implications for the entire government.
I thought of alerting him to the virtues of the sound-blocking headphones that many of my recent foreign clients sported.
