"Zerod attacked Knochyman and set off its Alarm Sentry Trap!"

When I try to "Alert Legion" I get...

"You can only send an alert against players who have disabled, hacked, raided, invaded, or used an artifact on you in the last 24 hours."

usually when players have a planet under attack they alert on the planet for defense so probably that case wasn't really thought of. Anyway, you can probably punish that guy by yourself.

I can but I haven't gotten to alert on anyone in so long that I was really looking forward to it.

you cant alert someone for just tripping a trap. this was intentional.

your a big boy, you dont need to be alerting just because you can. i personally take pride that i dont ever need to send out an alert for help. if i do send out an alert, the target must have done something to really piss me off and i cant retaliate fast or hard enough myself. my alerts i send out WILL get attacked brutally, so i reserve that for "special" cases.

It was because I was gone all weekend so I couldn't get online and retaliate myself.

But still, he attacked my planet so why can't I alert on him????

This is exactly what I do. Thankfully no one has made me angry yet. In fact, I was once hacked by 5 people in a row. using my vast stores of artifacts, I hacked or disabled them all myself. I came back with more research.