Infrared LEDs are perfectly safe to look at. They're what are used in most remote controls, for instance, as well as on many "night vision" surveillance cameras. Some very bright infrared LEDs can be seen as very dim red light, but anything smaller is typically invisible.

Infrared LEDs are perfectly safe to look at. They're what are used in most remote controls, for instance, as well as on many "night vision" surveillance cameras. Some very bright infrared LEDs can be seen as very dim red light, but even these are not harmful -- and the LEDs in a smoke detector will be much smaller than that.