Abstract: In some examples, a sensor node is mounted to a post and includes a microphone that is coupled to the post. The sensor node records, at a first time, first audio data, using the microphone, filters the first audio data to create first filtered audio, records, at a second time that occurs after the first time, second audio data using the microphone, filters the second audio data to create second filtered audio, and determines a difference in decibels between a first volume of the first filtered audio and a second volume of the second filtered audio. If the sensor node determines that the difference in decibels is greater than a predetermined threshold, then the sensor node sends a notification of activity that includes the difference in decibels.