Mud tubes on the foundation
Desert subterranean termites build pencil-width shelter tubes of soil and saliva up foundation walls, piers, and inside garage corners. A tube that crumbles to reveal live insects is an active infestation.
Hollow or blistered wood
Tap baseboards, door frames, and window sills. Termite-damaged wood sounds hollow and may show a thin blistered surface where the insects have eaten to within a paper's thickness of the paint.
Swarmers and discarded wings
After summer rains, winged reproductives leave the colony and shed their wings near windows and light fixtures. A pile of identical translucent wings on a sill is one of the most reliable indicators of a mature colony nearby.
What to do next
Do not disturb active tubes before an inspection — it scatters the colony and complicates treatment. Schedule a licensed termite inspection, which in Arizona should include a WDIIR-style written report of findings.