vB Easy Archive - Do cell phones light up for no reason?

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Do cell phones light up for no reason?
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Posted by: Robert Gift

Our Motorola 3-Watt Attache phone would light up as though a call were coming in. But no call was being received.

To trigger a tornado siren test, I want a photocell to detect a datebook event lighting up the cell phone at Noon every first Saturday of the month.

Will the cell phone light up for any other reason, such as a power interruption?
The phone would be on it's charger 24 hours.

When the datebook event alerts, does it need acknowledgement or it will give another alert until acknowledged?

Thank you

Posted by: Vagabundus

I am not an electrician. Not even an electronicician.

However I have a long history of electronic devices of all sorts doing strange things for no apparent reason. Thus I would not want to base any sort of non-double-checked emergency system on the assumption the cell phones will behave as directed.

It is possible, however, that I am just one of those strange cases. It might be that no one else has stood in front of repair/sales people with an electronic device doing something said person swore was impossible.

Given the use of printed circuit boards and lots of tiny little electrical devices that expect their electrical dose to come in micro-amps, and given the sheer amount of potential static-electricity-producing devices found just about anywhere, AND the sensitivity of devices trying to figure out just what that "almost-signal" burst was really about (whether its source was a cell or a frequency-jumping signal from some outlaw radio station or overenthusiastic amateur radio operator) I would predict lots of false alerts.

I believe that the stronger your base signal from your nearby cell transmitter the less likely some other ghost signal will set the device off. On the other hand, you might not care so much about false positives as you do about false negatives (i.e., there is a tornado alert and the strange electrical stuff in the air around the tornado-spawning clouds could cause the cell phone signal to fade away. . .)

I hope a real expert will chime in here. . .

Posted by: Robert Gift

Thanks Vaga.

I want to use just the Datebook of a disconnected cell phone to trigger a monthly test - first Saturday of the month at 12:00:00 CUT (GMT)

The cell phone would be in a shielded metal box to keep out light.

But I share your concern.
If a spurious signal causes the phone dial to light, the siren will sound.
Perhaps the cell phone would light to display NO SIGNAL warning!

I had better design a circuit to detect the beep the cell phone emits with it's visual Datebook event alert.
But I'm afraid any sound, like bumping the box, may activate the siren more easily than dial light.

Best would be to connect a telephone answering machine to the landline
in the building where the siren manual switch is located.
Only when the correct playback code is received, the answering machine goes into REWIND, which closes a relay to close another relay which closes the siren motor switch.

In case of a tornado, the switch is activated manually.

Posted by: Vagabundus

By the time you are through, you just might have a winning entry for the Rube Goldberg competition held at Purdue every year!

(I didn't expect the hamster's pacemaker to malfunction just because the container lit up from the energy differential which came about due to the cat's long hair and its tendency to rub against the small piece of silk that somehow worked its way into the cage through a small crack in the box where the welding joint failed . . .)

Long ago a friend of mine reported to our "PC Users' Group" that when returning from a short vacation he couldn't find the wall mounted phone. Eventually he found it--lodged underneath an upholstered chair about 30 feet away!

Apparently a lightning strike at a telephone pole had sent a "significant" current through the phone line (melting cord as it went) and literally blew the phone off of its wall jack. . .he reported that his computer RAM was fried--literally melted onto the motherboard--as the current blew right through the silly on/off switch (what's an inch or so to that many volts pushed by that much amperage?).

Apparently the circuit breaker on his MOS-protected power strip still worked just fine--isn't there a Murphy's law about the likelihood of a $100 sensitive part melting in order to protect the $0.04 fuse?

That was the incident that led me t respect "Acts of God." They can truly be spectacular!

Best wishes for your project--be sure and let us know when you're finished--extra credit for pix!

Vagabundus

Posted by: cmantito

if you just need to have something on a date/time rotation schedule trigger the switch the siren, why not just get one of those 7-day plugin timers that let you specify what time each day you want it to go off, set it to go off the one day you want it to and connect it up.

Posted by: Robert Gift

Yes, a 7-day digital appliance timer would do it.
Switch in the timer on Friday before the Saturday Noon test.
If our department is called out before Noon Saturday, the siren will sound accurately at Noon.
On return, switch out the timer. If no fire call, paid personnel switch it out on Monday.

It is extremely difficult to protect against lightning. Also, we should not test if threatening weather, anyway.

Better to skip my automatic test than have the siren sound at a wrong time.

Eventually, our mechanical siren is to be connected to a radio receiver which would trigger when Aurora Fire Dispatch sets off their electronic sirens.
When their electronic siren closest and southwest of our siren is triggered, our siren would sound.
But even though each Aurora siren can be individually addressed, Aurora sets off ALL their sirens for a tornado in just one area.
Sirens in our area of Aurora alerted for a tornado in the extreme south end of the City, though we were under clear blue skies!

Thanks.