This system uses a reliable relay base w/ relay, which makes routine checks a bit easier.
TQ2-L2-6V NAIS ATQ222 AROMAT RELAY TELECOM DPDT 1A 6V
You will find that this unbranded relay fits standard sockets, and the metal tabs feel secure and nicely finished.
A nice touch is the sturdy casing on this unbranded relay, which feels solid without any rattles inside.
A nice touch is the gentle tension in the terminals on this unbranded relay, which grips wires without crimping them hard.
The Omron branding adds a nice touch, signaling quality you can trust at first glance.
People often mention Omron for consistent quality, and this unit lives up to that expectation.