Background: Having high or low sound level inside and/or outside mosques is a frequent complaint from many people in Saudi Arabia. Currently, there is no standard optimizing the noted sound levels. Objective: The objective of this study was to measure the sound levels inside and outside 12 randomly selected mosques in Riyadh, Saudi Arabia. A secondary objective was to examine the reliability of using mobile phones as sound meters. Methods: Because mosques have different sizes, two “relative” locations were selected to measure sound from. For the inner sound, the location of the prayer leader “Imam” was chosen. Because the first neighbour is potentially most affected by the outer speakers, the outer sound was measured right next to that particular location. These two measures were collected from each mosque. For the secondary objective, sound levels obtained by two mobile phones were compared against a reference sound meter in an isolated room. Results and Discussion: Mean inner and outer sound levels (in dB) were 73.6 and 77.8, respectively. Mean difference between sound levels obtained by the two phones and the reference device was  1.1% suggesting a reasonable reliability level. The study highlights a need for developing acceptable levels for mosques sound.