An emergency notification system for providing information at an outside of a building regarding emergency events occurring inside the building, comprising a set of sensors arranged at a plurality of sensor locations inside the building, a set of indicators arranged at a plurality of indicator locations, such that optical or thermal signals emitted from the indicators are detectable from outside the building, and a timer , a. wherein each sensor is associated with a nearby indicator, b. wherein each sensor is configured to detect a predetermined sound related to an emergency event, and to transmit event information to its associated indicator, in response to detecting the predetermined sound, c. wherein each indicator is configured to receive event information from its associated sensor and to emit a first optical or thermal signal, in response to receiving event information, d. wherein each indicator is configured to receive a timer signal from the timer and to change a property of the first optical or thermal signal based on the timer signal, such that the set of indicators together form a time variant indication, detectable from outside the building, of sensor locations in the building where the predetermined sound is detected, e. wherein the set of indicators are connected in a mesh network , f. wherein a first indicator within the set of indicators, upon receipt of event information from its associated sensor, is configured to send a mesh network message to all other indicators in the mesh network, g. wherein a second indicator within the set of indicators, upon receipt of the mesh network message, and in case the second indicator is currently not emitting the first optical or thermal signal, is configured to emit a second, time-invariant, optical or thermal signal, different to the first optical or thermal signal. a. wherein each sensor is associated with a nearby indicator, b. wherein each sensor is configured to detect a predetermined sound related to an emergency event, and to transmit event information to its associated indicator, in response to detecting the predetermined sound, c. wherein each indicator is configured to receive event information from its associated sensor and to emit a first optical or thermal signal, in response to receiving event information, d. wherein each indicator is configured to receive a timer signal from the timer and to change a property of the first optical or thermal signal based on the timer signal, such that the set of indicators together form a time variant indication, detectable from outside the building, of sensor locations in the building where the predetermined sound is detected, e. wherein the set of indicators are connected in a mesh network , f. wherein a first indicator within the set of indicators, upon receipt of event information from its associated sensor, is configured to send a mesh network message to all other indicators in the mesh network, g. wherein a second indicator within the set of indicators, upon receipt of the mesh network message, and in case the second indicator is currently not emitting the first optical or thermal signal, is configured to emit a second, time-invariant, optical or thermal signal, different to the first optical or thermal signal. <EOS>