Is there another modern card that functions like Intruder Alarm in that I can untap a creature if another creature comes into play. I know there are plenty of creatures where I can tap it to untap another. But those don't combo well.
There is not a copy of intruder alarm in modern... or in magic I believe. However, if you are making a funzies deck you could make some convoluted combo that does the same thing. Like cloudstone curio, 3 mana dorks, and 2 village bell ringers. But generally 6 cards combos dont tend to see competitive play.
Cacophodon
Chandra, Fire of Kaladesh
Cinder Pyromancer
Deep-Slumber Titan
Devoted Druid
Dross Scorpion
Famished Paladin
Galvanic Juggernaut
Grimgrin, Corpse-Born
Karrthus, Tyrant of Jund
Lobber Crew
Merrow Levitator
Merrow Bonegnawer
Merrow Reejerey
Nettle Sentinel
Nettle Drone
Traxos, Scourge of Kroog
Village Bell-Ringer
Not sure what you meant, but something or some things from this list might work for you.
Tooth & Nail........Grishoalbrand....Living Dominance....Tezzerator.........Vannifar Pod
My Decks that have been BANNED
DRS Jund | Kiki-Pod | Bloom Titan | Splinter Twin | KCI