How do you make sentry guns in armory on evil genius?

In "Evil Genius," to make sentry guns in the Armory, you need to first unlock the appropriate research in the Tech Tree. Once you have the required schematics, go to the Armory and select the option to build a sentry gun. Ensure you have enough resources, such as money and materials, to complete the construction. After building, you can strategically place the sentry guns to defend your lair against intruders.