Give a message when a wand of secret door detection reveals something.

The Orb of Detection confers passive detect unseen: every few turns when carried it triggers the effect of zapping a wand of secret door detection for free.

Amulets of ESP occasionally randomly cause a detect unseen effect, because extra-sensory perception is more than just telepathy.

A lamp with the same unidentified appearance and base cost as a magic lamp. It is a charged magical tool (has a lifetime, comparable to an oil lamp) that sheds no light, but instead detects unseen in its range whenever it is turned on. This includes invisible monsters, secret doors, and all traps. It also allows vision to penetrate through clouds.