Instruction: Answer the given question by extracting information from the supporting document.

Input:
Question: How do I activate the preheat option of this mattress pad?
Document: This heated mattress pad has a great range of heat options, and works very quickly. I find the highest option to be quite toasty. The lowest option is definitely perceptible, and is best suited to taking the chill off your sheets. I especially love the dual side option, as my husband is always warm and doesn't want the extra heat at all. My side can be cranked up all the way, with no heat "leaking" over to his side.
This is one of the best purchases I have ever made! The mattress pad delivered everything it promised based upon other written reviews. It fits great on our mattress which is 15"+ and it is very comfortable to sleep on. The dual controls are wonderful and it is so awesome to climb into a toasty warm bed in the wicked cold winter months. We do preheat the pad each night and then turn it down to about 2 for the remainder of the night.
The heated mattress pad works perfectly and the controls are very easy. The only issue I've found is that when my husband has his side turned on and my side is off...I am getting residual heat from his side. Not a 'bad' thing - we're saving electricity by not having BOTH sides on, I guess... :)  My husband giggles every night when I preheat his side and then he crawls in about 20 minutes later. I highly recommend this.
I just received this mattress pad today. I put it on my sons bed at 6pm and turned it on high to preheat like the reviews suggest. We left the house to go trick or treating and I worried the whole time that it would burn the house down or be so hot my son would have to wait for it to cool down. My worries are for nothing it seems. The bed was barely warm in one spot down the center of the bed. What a let down for myself and my son.
My husband was using a heating blanket, and my mother recommended this as a different option. She bought one and loves it. So, we purchased this warming pad - and it's made life wonderful! I like my side of the bed cooler, but not freezing when I get in it. My husband loves it super-hot when he goes to bed. With this system, we have the best of both worlds!
Bought this to replace a failed unit. Works well, maybe too well. Has a range of Lo to 9 and I have never used it above a 2. Good plug attachment and lighted display. Always provides a &#34;preheat&#34; function when turned on. Very this wires that cannot be felt. Generally like this but have not yet run it through the washer dryer (torture test for heated mattress pads).
Preheat the pad to high and in 15 minutes crawl into bed and enjoy the extra heat brought out by the pillow. I turn mine off after about 15 minutes, I find that I get too hot to sleep when left on, but that first 15 minutes of not having to get into a cold bed helps me get to sleep so much faster its worth every penny.
I do find it to a little too warm, even on the low setting, but it is still worth every penny just to preheat my side before climbing into bed. I still love it! My wife, who is always cold, leaves it on "5" or "6" all night long with no complaints.Overall this thing is awesome! I would rate it as one of our best ever purchases. The wires in the pad are indetectable.
Warm, hmmmm, better described as HOT. I did the recommended set the controls on HIGH for 30 mins before bedtime. Well for me it was too warm when I went to bed. After a couple of days I would preheat the bed at a 3 or 4. I then turned it down to LOW or 1 for the night. My wife, who loves it HOT turns hers down to 3-4. This pad does the job. Buy it with no reservations.
We turn the pad on an hour or so before bedtime, on regular, not preheat, and the bed is toasty warm at bedtime, no cold spots.
Answer: It a precondition feature, you just turn it on by hitting a little button under the number level display which I do as part of my night time ritual as I get ready for bed. You adjust it to your own comfort level. I have mine as 2. When it is the coldest outside, 3 is the highest for me.