An acoustic shriek is an unexpected high pitched tone or other noise (either soft or loud) that may occur over phone networks.
Here's some advice on how to minimise the risk of acoustic shrieks on your phone line, as well as what you should know about making calls during thunderstorms.
Unexpected loud noise from telephones, especially when using a headset, may cause acoustic shock. These unexpected loud sounds may be caused by feedback, power fluctuations, fax tones, or signalling tones.
Acoustic shock may cause various physiological and psychological effects, including but not limited to:
On very rare occasions acoustic shrieks may cause hearing damage, however, in most circumstances any hearing impairment is usually a temporary side effect of the shock.
If you experience any of the symptoms described above as a result of an acoustic shriek, avoid driving and consult a doctor.
To minimise the risk of acoustic shock, we recommend that you follow these steps:
You may suffer an electric shock using your phone, fax, computer or other electrical equipment during a thunderstorm. In extreme cases this may be fatal.
If you must use your phone during a thunderstorm because of an emergency, then to reduce this risk:
When indoors, hands-free and cordless phones can be used safely if they're not touching the base unit. Mobile phones can be used as long as the phone isn't on a charger or connected to an external aerial.
When you're outside in a thunderstorm, the Australian Lightning Protection Standard (AS1768) recommends you don't carry metallic objects such as umbrellas, and you remove metallic jewellery, particularly from the upper body. Similarly, Telstra recommends against using a cordless or mobile phone outdoors in an unprotected area.
However, a handheld mobile phone may be used in a metal bodied vehicle with a metallic roof, provided there are no electrical connections (charger, external aerial etc.) to the phone. It may also be used with a hands-free car kit as long as the user is not touching the phone or kit and has no electrical connection to the phone. Using a Bluetooth wireless connection is another example of safe use when in such a vehicle. Of course, always obey the road rules.
The Australian Lightning Protection Standard also recommends that you don't use a fax, computer, or other mains powered equipment during a thunderstorm. However, a battery powered (e.g. laptop) computer with a wireless connection may be used.
Protective devices¹ can be fitted to phone installations to reduce the risk of personal injury during thunderstorms, but due to the high voltage involved in lightning strikes complete protection can't be guaranteed.
These devices aren’t intended to protect the equipment itself from lightning damage. For protection of your equipment contact the manufacturer or consult a lightning protection professional. Except for standard phones rented from Telstra, we don’t accept liability for lightning damage or power surge damage to any customer-owned or rented equipment associated with the phone service. Learn more about lightning protection in this short Telstra brochure about lightning surges (PDF, 66KB).
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