Step by step

  • Empty the crib and place the phone flat on the mattress, microphone unobstructed, case removed if possible.
  • Leave the sound machine in its real position at the setting you actually use.
  • Run a 30-second check. Short samples jump around; a 30-second A-weighted average is what the AAP-style guidance expects.
  • Write down the setup: distance, dial position, sound type, and which phone measured.
  • Adjust and repeat until you find the lowest setting that still masks the house.

Why most phone meters get this wrong

Generic decibel apps often use the default voice-processing audio path, which compresses and filters the signal before the app sees it. Apple provides a measurement mode that disables most of that processing, but few consumer apps use it, and fewer publish how far their readings drift from a reference meter on each model.

A second problem is physics. If the same phone is playing white noise, its microphone sits beside its own speaker. Whatever it reports is the level at the phone, not at the crib. That is the reason Lullasure separates the two jobs across two iPhones.

When to use the NIOSH app instead

For general-purpose workplace-style measurement on iPhone, the free NIOSH Sound Level Meter is the authoritative recommendation and includes calibration support. Lullasure is narrower: it is built for the nursery and for parents in loud places, with infant-specific guidance and a sleep-sound player attached.

Sources

Follow-up questions

Does the phone need to be inside the crib?

Only during the check, with the crib empty. Remove it before the baby goes in. Never leave a phone or cord in a crib.

Do I need a case off?

It helps. Cases that cover the microphone ports can lower readings by several dB.