Ancient Sentry Towers are extremely powerful and dangerous machines that appear in Phoenotopia and Phoenotopia Awakening. They resemble statues with the same blue design as other ancient technology such as the Scrappers. They were designed to keep intruders out of high-security areas. As such, they're only seen in the Ancient Crater and in a few secret areas.
Ancient Sentry Towers are tall structures with an eye-like crystal on the top which starts turning red when approached. If Gale gets too close, it will zap her with high-damage lasers until she is back out of its range. Any projectiles launched within the Tower's range will also be destroyed in the same manner.
The only way to destroy an Ancient Sentry Tower is to deactivate it by shining the Artifact's beam into the crystal at the top of the tower. The Tower will slowly shut down, but once it does it will send out sparks along the ground that must be dodged as being hit by them also deals heavy damage. The Tower will send out these sparks three times, each time sending two sparks going outward left and right.
Ancient Sentry Towers return in Phoenotopia Awakening, now known as Megaliths. Their rate of fire is slower in this game and they now prioritize shooting at foreign projectiles over shooting Gale herself, so it's possible to get past a Megalith even without the Artifact by distracting it with projectiles and sneaking by while it fires at the projectiles.