Reference an object where the key has bracket

Question

When I dump the result ($items) this is the "tags" object:

["tags"]=> object(stdClass)#20 (1) { 
    ["number::[Device]."]=> string(3) "381" 
}

I need that value "381" but how can I reference it?

this is the array i'm creating to send to the database:

  foreach ($items as $item) {
            $arg = array (
                @$item->id,
                **@$item->tags->{Number::[Device].}**,
                @$item->presentation->name,
                @$item->model,
                @$item->reportedTimeZone,
            );

I have tried a number of things but I either get an error or NULL.

Thanks.