The measurement of the levels of 222 Rn was accomplished during autumn to spring season in 2014 at residences distributed throughout 30 districts of Lima Metropolitan Area, including the north, centre and south areas of the city. The houses where the measurements were achieved were selected considering several variables as type of construction, age, construction materials, coatings, soil type, occupational use of rooms monitored, etc. For all the measurements of 222 Rn passive detectors was used (Solid State Nuclear Track Detectors SSNTDs) of cellulose nitrate (LR-115). Procedure and data acquisition are described and results; this monitoring is the first realized in this city. The results are only indicating the presence of 222 Rn, the detectors used do not allow to the discrimination of its descendants.