In order to get the Outdated Tech trophy in Far Cry 6, you first need to get the Techmaster Band wrist gear, which is the only way you can sabotage alarms. The most reliable (although not the cheapest) way to get the Techmaster Band is to buy it with Yaran Pesos from a fully upgraded Bandidos Barracks. If you don’t have enough metal and medicine to upgrade your barracks that much, the best places to get large quantities of camp resources are Los Bandidos operations and convoy hijacks. You might also be lucky enough to randomly find the Techmaster Band in a crate, during a Treasure Hunt, or for sale at a Juan’s Arms Dealer.
Once you’ve got the Techmaster Band, you’ve done the hard part. All you have to do next is equip the band, then find an FND installation to infiltrate. Sneak in, find an alarm and, instead of disabling it, hold the button displayed to sabotage it. Now you can stop sneaking and go loud. Shoot stuff, set off explosions, run around in the open – whatever it takes to get the soldiers’ attention. Once they’re alerted, it shouldn’t be long before one of them comes to trigger the alarm and gets blown up.