Hi Frank,
(Calculated)ContactStatus is a device attribute on the Data Aggregator, and can be retrieved from http://DA:8581/rest/devices/Device_ITEMID_DA.
For reachability, you may consider an openAPI query that retrieves the avg reachability for the last hour, such as
http://DA:8581/odata/api/devices?$apply=groupby(reachabilitymfs/ID, aggregate(reachabilitymfs(im_Reachability with average as Value)))&&resolution=RATE&period=1h&$select=ID,Name&$filter=((ID eq 6194))
Hth,
Lutz.