Pitch is only one part of protection. Placement and food access matter.
Young listeners may hear up to about 20 kHz. The upper limit often falls with age.
Their approximate hearing range extends from about 200 Hz to roughly 70–90 kHz.
EchoRepel sweeps 8–56 kHz. The lower end is audible to many people up close.
Ultrasound is directional. Closed doors, furniture and panels can leave sheltered pockets.
An app cannot make its speaker produce strong ultrasound. A frequency slider proves little.
Keep the grille clear. Combine with food control, barriers and regular inspections.