Should a smoke alarm be installed in the attic

I left it off for a time, and did not notice any more water coming from the opening in the ceiling

I'll bet there's cold air from the attic coming through that hole, mixing with warm air in the living areas in your house and causing condensation to build up in the smoke detector.

You should seal that hole (a) to prevent cold air from moving down, and (b) to prevent any smoky air (should you be unfortunate enough to have any) from being pulled up through it (a process known as the Stack Effect , which can reduce the effectiveness of smoke detectors.

A proper electrical box is the only way to do this. You CANNOT simply cut a hole and pass the wires through. Any and all line voltage (120/240V and up) splices must be in an approved box and be accessible, meaning you cannot bury a junction or splice box. I could cite all sorts of relevant codes but I don't think that's necessary. This should be obvious.

Here is a recent thread on this very subject: What type of electrical box do I use for a hard-wired smoke detector?

Remember, it is almost a certainty (code wise in the US) that an AFCI breaker is required.