Alerts on both devices

I’m sure there is probably an easy answer for this and probably a quick way to do it, but I feel like I have looked everywhere and cannot find it. Is there a way to get the watch AND the phone to alert when a notification pops up? Right now I’ll get it on one or the other and sometimes I don’t get it on either and I don’t know what causes that. However, I’m wondering if there is a setting that can be turned on that will allow the watch to still alert when the phone does and the phone to still alert when the watch does.