A building control system, comprising; a mobile tag (101, 700), wherein the mobile tag operates to move within a structure; a plurality of first sensors (121, 122, 123, 124, 125), wherein the plurality of first sensors operate to sense a first condition of the structure; a plurality of second sensors (131, 132, 133, 134, 135), wherein the plurality of second sensors operate to sense a second condition of the structure; a controller, characterised in that the controller operates to: generate a first set of weighted likelihoods based on the first sensed condition of the structure, wherein the first set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of a plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure, wherein the grid points provide an overlay that section up the structure and each grid point represents a different location within the structure; generate a second set of weighted likelihoods based on the second sensed condition of the structure, wherein the second set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of the plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure; generate a combined set of likelihoods based on the first set of weighted likelihoods and the second set of weighted likelihoods, wherein the combined set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of the plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure; and estimate a location of the mobile tag (101, 700) within the structure based on the combined set of likelihoods. a mobile tag (101, 700), wherein the mobile tag operates to move within a structure; a plurality of first sensors (121, 122, 123, 124, 125), wherein the plurality of first sensors operate to sense a first condition of the structure; a plurality of second sensors (131, 132, 133, 134, 135), wherein the plurality of second sensors operate to sense a second condition of the structure; a controller, characterised in that the controller operates to: generate a first set of weighted likelihoods based on the first sensed condition of the structure, wherein the first set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of a plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure, wherein the grid points provide an overlay that section up the structure and each grid point represents a different location within the structure; generate a second set of weighted likelihoods based on the second sensed condition of the structure, wherein the second set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of the plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure; generate a combined set of likelihoods based on the first set of weighted likelihoods and the second set of weighted likelihoods, wherein the combined set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of the plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure; and estimate a location of the mobile tag (101, 700) within the structure based on the combined set of likelihoods. generate a first set of weighted likelihoods based on the first sensed condition of the structure, wherein the first set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of a plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure, wherein the grid points provide an overlay that section up the structure and each grid point represents a different location within the structure; generate a second set of weighted likelihoods based on the second sensed condition of the structure, wherein the second set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of the plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure; generate a combined set of likelihoods based on the first set of weighted likelihoods and the second set of weighted likelihoods, wherein the combined set of weighted likelihoods includes a weighted likelihood of the mobile tag (101, 700) being at each one of the plurality of grid points (110, 111, 112, 113, 114, 115, 116, 117, 118, 119) within the structure; and estimate a location of the mobile tag (101, 700) within the structure based on the combined set of likelihoods.