A method including recognizing at least one gesture to define at least one computer-implemented virtual boundary in a monitoring space, wherein the gesture includes a motion along a path and at a location in a monitored scene space wherein there is a correspondence between the monitoring space and the monitored scene space; causing implementation of the at least one virtual boundary in the monitoring space corresponding to the scene space, wherein at least part of the virtual boundary is determined by the path in the monitored scene space and the at least part of the virtual boundary is located in the monitoring space at a corresponding location equivalent to the path location; and processing received data to generate a response event when there is, relative to the at least one virtual boundary, a change in a portion of the monitored scene space.