These sites provide royalty-free options suitable for personal projects or independent creators:
Night Vision Optics Toggle On-Off - Sound Effects - Motion Array night vision sound effect download
A sharp, metallic "click" or "thunk" as the unit is switched on or flipped down. night vision sound effect download
A rising high-frequency tone that mimics a capacitor charging, similar to an old camera flash. night vision sound effect download
Depending on your project's budget and licensing needs, several platforms offer high-quality audio files in various formats like WAV and MP3. Free Resources