diff --git a/README.md b/README.md
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--- a/README.md
+++ b/README.md
@@ -1,5 +1,31 @@
 # phosphor-fan-presence
-Phosphor fan provides a set of fan monitoring and control applications.
+Phosphor fan provides a set of fan monitoring and control applications:
+
+## Fan Control 
+
+Sets fan speeds based on configuration data.
+
+## Fan Presence Detection
+
+Monitors for fan presence using either GPIOs or nonzero tach readings or both.
+
+## Fan Monitor
+
+Compares actual fan speeds against expected ones and takes actions.
+Additional documentation is [here](monitor/README.md).
+
+## Cooling Type
+
+Sets the cooling type property in the inventory based on a GPIO.
+
+This is not built by default, use --enable-cooling type to enable.
+  
+## Sensor Monitor
+
+Takes actions based on sensor thresholds and the like.
+Additional documentation is [here](sensor-monitor/README.md).
+
+This is not built by default, use --enable-sensor-monitor to enable.
 
 ## To Build
 By default, YAML configuration file(s) are used at build time for each fan
diff --git a/sensor-monitor/README.md b/sensor-monitor/README.md
new file mode 100644
index 0000000..2887c53
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+++ b/sensor-monitor/README.md
@@ -0,0 +1,19 @@
+# Sensor Monitor
+
+This application can take action based on sensor thresholds and values.
+
+## Available Monitors
+
+### ShutdownAlarmMonitor
+
+This monitor will watch all instances of the
+`xyz.openbmc_project.Sensor.Threshold.HardShutdown` and
+`xyz.openbmc_project.Sensor.Threshold.SoftShutdown` D-Bus interfaces for the
+alarm properties to trip.  When this happens, a configurable timer is started
+at the end of which a power off is executed if the alarms haven't reset by that
+time.  Event logs will also be created.
+
+The configuration options `SHUTDOWN_ALARM_HARD_SHUTDOWN_DELAY_MS` and
+`SHUTDOWN_ALARM_SOFT_SHUTDOWN_DELAY_MS` can be used to change the delays.
+
+Currently, this monitor is enabled by default.