A standard term is geodetic coordinate system. However, the market leader in GIS software tends to invent new terminology with each new release of its flagship system, and by virtue of gaps in fundamental training by most of its users (or just plain enthusiasm for new words), this terminology quickly gets adopted by the majority. For example, "Geographic coordinate system" was newly introduced with ArcGIS 8 about ten years ago but AFAIK it was not in common use before then.
To a high relative accuracy, in this application--where the region to be mapped will not extend more than a few hundred meters and it is not near either pole--you can treat lat-lon as a Cartesian coordinate system that uses two different linear units of measure.
Each degree of latitude will be approximately 111300 meters (and a more accurate value, which may differ from this by up to a few hundred meters, can be found once and for all by consulting tables or through a preliminary calculation). Each degree of longitude will be approximately 111300 * cos(latitude) meters (with the same possibility of making it a little more accurate with a little more preliminary work). For the latitude in the equation use the latitude of the middle of the building. The errors will be much smaller than one meter.
For example, suppose you locate an object 10 meters west and 20 meters north of a sensor at (lat, lon) = (45.000100, 6.500000) and the building's center is at latitude 45 degrees. Since cos(45) = 0.7071068, each degree of longitude is worth 111300 * 0.7071068 = 78701 meters. Therefore the object is displaced 10/78701 = 0.0001271 degrees west (which is the negative direction) and 20/111300 = 0.0001797 degrees north. This would locate it at (lat, lon) = (45.000100, 6.500000) + (0.000180, -0.000127) = (45.000280, 6.499873).
Assuming the sensor locations are perfectly accurate, note that even a 5% error in these particular calculations would still place the final coordinates within 5%*20 = 1 meter of their correct locations. That's why there's no need to be finicky about accuracy in the conversion from meters to degrees: one part in a thousand would be more than good enough for any building.
(For advice on precision in these coordinates please see Measuring accuracy of latitude and longitude?.)
Best Answer
It depends on what you mean by 'Universal Coordinate System'. If you wonder whether most Professionals understand Latitude and longitude, well in that case it is pretty much universally understood.
But if you ask, whether it is used by everyone, then the answer is a resounding, No. There are many reasons why people use projected coordinate systems instead of a Geographic Coordinate system, such as:
Amongst those people who use Geographic systems, there may not be universal agreement about what reference system to use. There are different datums that one could use, as well as different prime meridians that could be used. This comes into play, if you are searching for long lost treasure, or if you go to the Greenwich Observatory with a GPS and wonder why you are not at 0 longitude