A security monitoring system including: a system controller; a video camera arrangement , coupled to a motion sensor , arranged to monitor a surveillance area; a portable token storing a token ID; the video camera being configured on receipt of a motion detection signal from the motion sensor to send an alert to the system controller; the system controller being configured in an armed state, on receipt of an alert from the video camera , to start an event timer and to send an instruction to the video camera to broadcast a token activation signal, the instruction including an event identifier; the video camera further being configured to, on receipt of the instruction from the system controller, broadcast a token activation signal including the event identifier; the portable token being configured to respond to receipt of a token activation signal from the video camera by broadcasting a response including the token ID and the event identifier; the system controller further being configured: on receipt of a response from the token to: compare the event identifier included in the response with the event identifier included in the instruction to the video camera ; compare the token ID included in the response with one or more stored token IDs; and to suspend the event timer if both comparisons provide a match; if either no response is received or one or both comparisons do not provide a match, to determine an alarm event on expiry of the event timer. a system controller; a video camera arrangement , coupled to a motion sensor , arranged to monitor a surveillance area; a portable token storing a token ID; the video camera being configured on receipt of a motion detection signal from the motion sensor to send an alert to the system controller; the system controller being configured in an armed state, on receipt of an alert from the video camera , to start an event timer and to send an instruction to the video camera to broadcast a token activation signal, the instruction including an event identifier; the video camera further being configured to, on receipt of the instruction from the system controller, broadcast a token activation signal including the event identifier; the portable token being configured to respond to receipt of a token activation signal from the video camera by broadcasting a response including the token ID and the event identifier; the system controller further being configured: on receipt of a response from the token to: compare the event identifier included in the response with the event identifier included in the instruction to the video camera ; compare the token ID included in the response with one or more stored token IDs; and to suspend the event timer if both comparisons provide a match; if either no response is received or one or both comparisons do not provide a match, to determine an alarm event on expiry of the event timer. on receipt of a response from the token to: compare the event identifier included in the response with the event identifier included in the instruction to the video camera ; compare the token ID included in the response with one or more stored token IDs; and to suspend the event timer if both comparisons provide a match; if either no response is received or one or both comparisons do not provide a match, to determine an alarm event on expiry of the event timer. <EOS>