It's possible that there is an issue with the key chip or the anti-theft immobilizer system in your 2009 Nissan Titan. The alarm going off and the truck not starting could be indications of a problem with the security system.
One possible cause is that the key chip has malfunctioned or been damaged, preventing the engine from starting. Another possibility is that the anti-theft immobilizer system has been tripped and needs to be reset.
To diagnose and fix this issue, it's best to take the truck to a Nissan dealership or a reputable mechanic who has experience working with Nissan vehicles. They will be able to run diagnostic tests on the security system and determine the root cause of the problem.
In the meantime, you can try disconnecting the battery for a few minutes to see if that resets the security system and allows the truck to start.