Silence is the best ally. Tuck the latch into a shallow pocket so the contact is muffled, and use a spring with adjustable tension—think of it like a metronome ticking just enough to feel, not to echo. Add a thin layer of rubber or felt between the moving parts; that will dampen any rattles. Keep it so the opener only hears a whisper of movement, like a breath in the dark.

Aim for about a millimetre or two in depth—just enough to hide the moving arm but still let the latch slide without snagging. Use a fine‑tipped caliper to dial in that clearance. For the weight test, hang a 5‑gram weight from the latch arm; if it swings silently, you’re good. Adjust the spring until the arm barely moves when that weight is released, then lock it in. Keep the whole assembly on the dark side of the door frame; it’ll stay unseen and unheard.

All set on my end. When you hit that weight, keep the door closed and let it sit—if nothing but a faint sigh passes through, you’ve nailed the whisper. I’ll stand by for the quiet verdict.