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Baby monitors

Babyfon
Baby monitoring systems comprise a baby unit and one or more parent units. The baby unit, installed in the infant’s room, is a transmitter (producing emissions), and parent units are mainly receivers. In some cases, however, both units are capable of transmitting and receiving. Most baby monitors do not transmit signals (produce emissions) continuously, but only when a certain sound level – set by the user – is reached in the nursery (e.g. voice activation).
Some systems also monitor whether the parent unit is still within range of the baby unit, by transmitting brief test signals (i.e. emissions) every few seconds.
A wide variety of baby monitors are available, with widely varying ranges and emission levels. Emissions from two systems with different transmitting powers were measured on behalf of the FOPH. They were found to decline very rapidly as the distance from the device increases, and to lie consistently below the recommended limit. At a distance of 20 cm, emissions from the less powerful device are 28 times lower and from the more powerful device 3 times lower than the recommended limit. At a distance of 1 metre, emissions are, respectively, 93 and 9 times lower than the recommended limit. Even if the device accidentally comes into contact with the infant during operation, the values for the systems tested are below the recommended limit. The emissions produced when a range-checking test signal is transmitted are much lower still.
On the basis of the available findings, emissions from systems of this kind are not expected to pose any hazard. It is, however, advisable to reduce the infant’s exposure to emissions as far as possible.
  • Place the baby monitor at least a metre away from the cot.
  • Do not use systems that transmit continuously. Set the baby unit to voice activation mode.
  • If the baby monitor is mains operated, ensure that the adaptor is plugged in at least 50 cm away from the cot.

Detailed information

1. Technical data

Baby monitors operate at a wide variety of frequencies, with corresponding differences in transmitting power and range (Table 1). For most of these frequencies, devices are not permitted to transmit continuously (continuous carrier); signals should therefore only be transmitted from a given sound level. Most monitoring systems are unidirectional, i.e. the baby unit can only transmit and the parent unit can only receive. In systems with a range-checking function, a signal is transmitted by the baby unit every few seconds to determine whether the parent unit is still within range. In some cases, this function can be deactivated. With bidirectional systems, where both units can transmit and receive, range checking can be performed using the parent unit, e.g. by pressing a button.
Certain systems also have a video monitoring function. These require a continuous carrier (e.g. at 2400 MHz) and produce emissions continuously.
The limits recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for electric fields depend on the frequency [1].

Frequency (MHz)
Wavelength (m)
Max. transmitting power (mW)
Max. range (m)
OFCOM designation
ICNIRP reference level (V/m)
27
11
100
 400
Wireless audio Baby monitoring
28
40,7
6,5
10
150
Gen. short-range radio devices
28
446
0,7
500
5000
Professional mobile radio
29
865
0,35
10
400
Wireless audio
40
1800
0,17
20
   
Wireless audio
58
1900
0,16
250
300
DECT
60
2400
0,125
10
300
Gen. short-range radio devices
61
Table 1: Frequencies used by baby monitors
Low-frequency fields
Baby monitors are battery or mains operated. In mains-operated systems, the adaptor is in operation even when the device is switched off. Frequently, a low-cost, inefficient transformer is used, producing substantial 50 Hz (stray) magnetic fields in the immediate environment. At a distance of 50 cm, however, these stray fields are very weak.

2. Exposure measurements

Exposure to emissions is best described by the specific absorption rate (SAR, in watts per kilogram), which is a measurement of the electromagnetic radiation (W) absorbed by the human body (kg). In appliances operated at least one wavelength away from the body, the electric field can be measured as a basis for calculation of the SAR.
In a study carried out by the IT`IS Foundation on behalf of the FOPH, electric fields were measured for two different baby monitors. Although baby monitors should not be operated close to the body, the SAR was also determined for both models [2]. For these measurements, a sustained tone was used to keep the devices operating continuously, producing the highest possible emission levels.
SAR values
The SAR values measured for the two baby monitors are shown in Table 2. In both cases, the value is well below the limit of 2 W/kg recommended by the ICNIRP [1].
  
Device
Frequency (MHz) 
Transmitting power (mW)
SAR (W/kg)
Baby monitor 1
863
10
0,01
Baby monitor 2
446 
500
0,08
Table 2: SAR values for two markedly differing baby monitors

Electric fields
The electric fields measured close to the devices during continuous operation are shown in Figure 1. It is striking that these are highly distance dependent. The field strengths measured are always below the frequency-dependent limits recommended by the ICNIRP (40 V/m for baby monitor 1 and 29 V/m for baby monitor 2) [1]. At the recommended operating distance of a metre, the fields are 0.43 V/m and 3.2 V/m respectively.
Elektrisches Feld von Babyfonen als Funktion des Abstandes
Figure 1: Electric field (E-field) over distance for two different baby monitors [2].

3. Health effects

Short-term health effects due to electromagnetic fields can be assessed on the basis of the limits recommended by the ICNIRP [1]. Since emissions from baby monitors are well below these limits, short-term health effects are not to be expected.
Little is known about possible long-term effects of weak high-frequency electromagnetic fields, such as occur in the vicinity of baby monitors. One way of responding to these uncertainties is, as a precautionary measure, to minimize exposure by ensuring that the recommended distance between the device and the infant is maintained, and by switching on the voice activation function.

4. Legal regulations

Specifications for the output power of baby monitors are included in the technical interface regulations (RIR) issued by the Federal Office of Communications (OFCOM).

5. Literature

1. ICNIRP. Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields up to 300 GHz. Health Phys. 75: 494-521. 1998. See "Further information"
2. Kramer A et al. Development of Procedures for the Assessment of Human Exposure to EMF from Wireless Devices in Home and Office Environments. 2005. IT'IS report. See "Documents"

Specialist staff: emf@bag.admin.ch
Last updated on: 01.09.2006

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