Cell phone as baby monitor
My partner and I were vacationing at a B&B with our 1-year old daughter. When she fell asleep at 8PM, there was plenty of evening left for the adults, but since we were all sleeping in the same room, we didn't bring our baby monitor. Her mother came up with this great hack -- our cell phones. We have free mobile-to-mobile calls, so no issue there. She put our daughter down, called me on my cell phone and left her phone near the pack-and-play. I put her call on speaker and muted my phone. Instant monitor, and we could sit out on the porch worry-free for a couple of hours.