There is a piece of wood under the mattress between where I need to place the Sensor Pad and the mattress

The Sensor Pad must always be placed under the mattress itself, in the middle of the cot, bedside crib.

To explain, the Sensor Pad detects your baby's movement on the full surface of their mattress from corner to corner - however small, subtle these movements are, including the rise and fall of the chest area.

These movements from baby transfer down to the Sensor Pad through the mattress.

The Sensor Pad has a collecting surface (the top) which transfers movements and concentrates them in the centre of the pad. The movements do not have to be directly on top of the pad as the mattress itself will transfer the vibration forces (but not quite so effectively).

These small vibration forces concentrated in the centre of the pad are detected by a Piezo Crystal. The crystal has the property of producing a small signal in proportion to the change in force applied to it.

When there is no movement / vibration from baby detected on the surface of the mattress, there is no change in force on the crystal hence, no output is produced - thus the monitor will alarm to alert you of this.

When there is movement / vibration from baby detected on the surface of the mattress, a signal is produced in sympathy with the movements - thus the monitor does not alarm.

When there is movement / vibration from baby detected on the surface of the mattress, the signal produced from the Sensor Pad goes into the Nursery / Camera Unit where it is magnified.

At this point as movement is being detected the monitor will not alarm.

If there is something that is hard such as a board fitted to the mattress, between the Sensor Pad and the mattress, the Sensor Pad would not be able to detect your baby's movements thus the monitor will alarm when not needed, baby is moving.

With regards to the recommended hardboard support in the manual, this is generally only required when:

• You are receiving false alarms; the board can help to improve contact between the Sensor Pad and baby's mattress allowing the pad to fully detect baby's movements
• The Sensor Pad is used in a cot with a slatted base as this acts as a stable base for your Sensor Pad to sit on

As baby grows and becomes more mobile around the cot the mattress is also prone to slight movement. The mattress can shift slightly causing the Sensor Pad to move slightly between the slats on the base of the cot. Thus you may receive false alarms.

The board that you use does not have to specifically be hardboard, however it does need to be flat and rigid.

That said we do know from talking to users daily that many use the Sensor Pad without a board and advise that the monitor is working effectively with no false alarms.

The minimum & maximum dimension for the board in the manual is as a guide but basically it needs to be larger than the area of the Sensor Pad.

The manual recommends:

• Thickness: 6mm
• Minimum dimensions: 33 x 33 cms

PLEASE NOTE: You would need to take into account that if you have a thin/soft mattress along with the Sensor Pad using a thicker board could push the Sensor Pad up into mattress.