Smote detector or CO detector

[2Vicars]

Trying to figure out what should go in this location or the group recommends for this spot. Something was there at some stage. Smoke detector or CO detector? This is in the hallway in front of the bathroom and leading to the bedroom Thanks.

2001 h3-45

[Gil_J]

It was a smoke or smoke/CO detector. Make sure a new one is installed as recommended. Smoke detectors should be as high as possible.