Xiaomi devices: how to get signal strength?

I’m using the Xiamoi Gateway v2 and some sensors. I have one outside in the mailbox, which connects fine with the Gateway, but loses the Connection over time. So I think the Signal isn’t strong enough to get to the Gateway everytime. But how can I check Signal strength? Didn’t see one in the MiHome App or in Channels/Things?
is there a way to get to something as a Signal strength?