Here's some information regarding the services:
GetAlertSummary : Gets the alert summary status for a Thing you are requesting. Can also see ack or non-ack alerts as well. (Current alert state)
QueryAlertSummary : Queries the alert summary. (Works the same as QueryAlertHistory).
QueryAlertHistory : Queries the alert history of data shape of alert history stream for a specific Thing. It can be used across org units, since there is only one alert history stream for the entire application.
Services are based on internal grids:
Alert Summary Grid: Summary list of all alerts and their status
Alert History Grid: Historical list of all alerts and their status