Interesting, I thought if my theory was wrong then the Doctor drugging them must've been the solution! I'm really intrigued to the answer now :)

My solution's still for the Biologist, though presumably it was wrong too: at around Midnight he killed the Andersons in their sleep, then returns to his room and sets his alarm for 11am to ensure he has an alibi of being found drugged asleep, then finally he takes the powerful 12 hour sleeping tablet (not during supper as he claims). And as drennan pointed out, if it's a wind-up alarm clock that he'd already set for '11' back at 8pm then it would have simply gone off during the night at 11pm. Unlike a 24-hour electronic clock that could deal with am/pm, wind-up clocks don't, so setting it for 11 at 8pm would have just disturbed everybody (or at least Allison) only 3 hours later, not 15, which didn't happen. That would prove he must have set his alarm some time after 11pm, which in turn prove his story and alibi is a lie.

(In fairness I had thought of that too, if entirely failed to explain it! :D It's why I said he might've meant to set it for 11pm, I meant that he then forgot to turn the alarm setting off so it also went at 11am. Otherwise, and more likely a reason, I assumed that he'd only set it after committing the crime to ensure his discovery in the morning drugged asleep to provide his alibi).

The only alternative I can think of comes down to whether you class a wind-up alarm clock as an electrical or mechanical device; if it's still electronic then we instantly know that Allison must be lying, as we know for sure nobody had brought or was allowed any electronic devices. Although that wouldn't really prove how she did it, just that she lied! :)