Do I need hardboard under a movement sensor pad in a slatted cot

Why do UK slatted cots give pads a problem that solid bases do not?

A movement pad needs even pressure against the underside of the mattress. On a solid, flat base the pad can sit still. On the slatted bases common in UK cots, Angelcare’s UK help says the mattress can shift as the baby becomes mobile and the pad can slip between slats — then you get alarms while the baby is still moving. Babysense’s false-alarm article says spring or wooden-slat bases cause irregular contact between pad and mattress.

The board is a manufacturer set-up part, not a general cot-safety extra. This page quotes the sizes the makers publish for their own pads. It is not a guide to cot bars, mattress firmness ratings or second-hand frames.

If a board is already built into the *mattress* (a fibre or wooden stiffener inside the cover), Angelcare UK says that layer sits between the pad and the baby and can stop movement reaching the sensor — so the monitor alarms when the baby *is* moving. The published board belongs under the pad, on the cot base, not inside the mattress stack above the pad.

What size board do the makers specify?

Angelcare’s install wording explains the job of the board: it keeps a constant pressure on the pad so the pad can still detect movement when the baby is at the edges of the cot. On a slatted base without a board, the same pages say to sit the pad so its edges are held over at least two slats.

How do I fit the board without blocking the pad?

1. 1
   Read the size line in *your* booklet first If it says 30 × 30 cm × 6 mm, do not substitute a Babysense-sized ½-inch ply ‘because bigger is better’ without checking thickness. Angelcare UK warns that a thicker board plus a thin, soft mattress can push the pad up into the foam.
2. 2
   Take the mattress out and look at the base Solid, stationary, completely flat: Angelcare’s install pages do not ask for a board. Slatted, sprung, or not flat: add the board. If you are not sure, the UK ‘piece of wood’ article says a board is generally used when you are already getting false alarms, or when the base is slatted.
3. 3
   Lay the stack in this order Cot base → hardboard → sensor pad (printed / logo side up) → mattress. That is the order Angelcare and Babysense both describe. Reverse the middle two and the pad is blind.
4. 4
   Keep the board larger than the pad, and the pad in the centre Angelcare: board larger than the pad’s surface area; pad in the approximate centre. Babysense Connect: two pads on the first and third quarters of the sleep surface, each on its own board, markings ‘THIS SIDE UP’.
5. 5
   Secure cords under the mattress, out of reach Babysense install notes: pull excess cord back under the mattress and cable-tie it so it is not visible or reachable. Angelcare: route the cord toward a corner, away from hands. This is the maker’s strangulation warning for the lead, not a general cot-standards lecture.
6. 6
   Run the empty-cot test before the baby goes back in For Angelcare, that is the four-corner test. For Babysense, the false-alarm article says to confirm a snug pad-to-mattress contact and a firm, not overly thick, mattress. Memory-foam mattresses are outside Angelcare’s published compatibility list.

What is the board not meant to fix?

• A next-to-me that is still attached to your bed. Angelcare UK says the pad then reads the adult. Separate the furniture — see pads in a Moses basket or next-to-me. A board will not filter out the adult.
• A moving pram or car. The Lullaby Trust’s false-reassurance note is about vibration, not about slats. A board in a moving chassis still shakes.
• A memory-foam or hollow-frame mattress. Angelcare’s help pages say those constructions do not pass movement down to the pad. The board sits below the pad; it cannot make dense foam transparent.
• SIDS risk. The Lullaby Trust says there is no research that movement monitors prevent SIDS. A correctly sized board is a signal-quality step, not a safer-sleep substitute.

In shortOn a slatted UK cot, the makers ask for a flat rigid board under the pad, not under the baby. Angelcare’s published figures are at least 30 × 30 cm × 6 mm, with some pages saying 33 × 33 cm — use the booklet. Babysense’s published figure is at least 43 × 28 cm × 1.2 cm under each pad. A board between pad and mattress is the wrong sandwich.