Unable to lock truck and set alarm; Intermittent problem

Update: It would appear that the double beep sound I hear when I'm unable to lock/alarm my Tundra is the same sound that one hears when the key is in the ignition AND a door is opened (Note: Not the shrill, continuous alarm that manifests when one tries to lock the truck with the key fob while a door is ajar). As I first mentioned, when this problem arose I replaced the ignition switch thinking that might be the problem (it was also acting a bit sticky, if you will). Perhaps the problem is with the key system but not the key cylinder per se. I'm starting to think that key cylinder must engage with another switching mechanism and that that mechanism is where the problem is happening. Just a theory for now.....

 

There is a switch at the back of the cylinder

 

@empty_lord: Thanks. I found a reference to the switch which seems to be aptly named the "Key unlock warning switch." Next time the problem occurs I'm going to see if repeatedly reinserting the key makes the problem go away. In the end, I suspect I'll just have to replace it but I'm curious.

 

Four days ago I disconnected the "Key unlock warning switch" and so far I've not had any problems, nor have I seemingly lost any important functionality. For obvious reasons the double beeps no longer occur when I open the door with the key still in the ignition. I'll provide an update should anything go awry in the future. Thank you all for your helpful hints. - Best - Jim