OtoBLE

To be sure that a custom earpiece for hearing protection shows optimal behaviour one can perform a fast leak test.
A proper test provides certainty about a perfect fit of the earpiece. When there is a perfect fit, noise can only enter the ear canal through the noise filter and not outside to the earpiece.
For that purpose the room in the ear canal, between eardrum and otoplastic, is brought to a small overpressure of 5mB (0,073 psi), by means of air.
When the pressure is reached, the air system is closed and when the pressure stays stable for five seconds the otoplastic has the perfect fit. The related software controls the earpiece tester and allows the user to analyze the pressure course, real time, by means of a graph.
There is an app for Windows 10 and iOS too.

Specifications
Test pressure : 5mB (≡ 51mmH2O of 500Pa)
Trip pressure : < 4mB
Test time : 5 seconds
Test duration : max. 10 seconds
Bluetooth® : version 4.0 (min.), LE, 10m range
Power source : 4 x AA battery Alkaline or NiMH
Dimensions : 154 x 96 x 34mm
Weight : approx. 250 gr. (excl. batteries)
Enclosure : black, PMMA (UL 94 HB)