We have studied a method of monitoring an indoor environment using an advanced robot vacuum cleaner equipped with a small sensor unit consisting of temperature, humidity, and gas sensors. We conducted a test to detect a vaporized material on the floor in a room. The sensor unit (temperature, humidity, air pressure, quartz crystal microbalance, and semiconductor gas sensors) was used in the test. Measurements were made with the sensor unit placed in the dust box of the vacuum cleaner. To represent a leaked liquid, a given number of water droplets and a sponge soaked with a given volume of ethanol were placed at different locations on the floor, and we investigated the detection characteristics of each sensor when the cleaner passed by the droplets and sponge representing the leaked liquid. In all the detection tests, measurements made with the sensor unit placed in the dust box showed the selective detection of water and ethanol. The most likely reason for the increase in detection output is that a few water droplets on the floor were distributed by the brush and vaporized to inside the robot vacuum cleaner, where they were detected by the sensor unit in the dust box. We showed that this form of monitoring has the potential to detect a spilled or leaked liquid.