Eclipse alarm battery is a CR2354
The battery in the Eclipse alarm base is a CR2354 coin battery available online or at good jewellery, photographic or electronics stores.
To change the battery in the DRI Sleeper eclipse simply open the battery compartment by inserting a thin object between the raised edges on the alarm case. Slide out the battery holder and remove the old battery. Replace the battery with a fresh CR2354.
Slide the battery holder shut before replacing the battery cover.