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.