BeBe Sounds brand Movement Sensor Pad with Sound Monitor.  The alarm sounds ONLY if absolutely no movement is detected for 20 seconds.  Place the sensor pad under baby's mattress.  If the baby stops moving/breathing for 20 seconds, an alarm will sound.  This helps give parents the peace of mind needed so they can also rest.  I had twin boys that were born prematurely and I used one of these for each crib.  Having these really helped me to rest better.  This also serves as a monitor, so no need to purchase an additional sound monitor.  I have sold one already, so have one more for sale.  I paid $89.95 for mine.  Most places online are currently selling this particular monitor for around $95.00.