Ring of see invisible
Wearing a ring of see invisible gives you see invisible, which lets you see creatures that are invisible. As invisible monsters are tricky to detect without other properties, this ring can be useful to tide you over until you can gain the property intrinsically. Wearing it constantly may not be necessary; just slip it on at first notice of a spellcaster turning invisible or assault by an unseen monster.
Dropping this ring down a sink while not blind produces the message You see some air in the sink.
