Hi,
I've been trying to understand how cellular communicators work, and I have
to admit, I'm a bit confused. From what I can tell from reading through
the
docs on the different suppliers (ie: Teleguard, Uplink, etc), they
communicate via GPRS over GSM. Which sounds reasonable given that there
really isn't a whole lot of data to transmit.
But here is where I get lost. For any device to communicate over GSM, it
needs a SIM chip, which implies that every device would require a unique
SIM
chip. Who provides the SIM chip? Does that come from the central
station?
Does that also mean that every device have a unique telephone number? ie:
if I knew the number, I'd be able to call the device directly? How is
that
profitable? The local companies here charge 15$/mth for cellular
monitoring. Assuming that the alarm system makes a verification phone
call
every night to the CS, that would imply at minimum 30mins of usage a month
(assuming per-min billing) not counting any additional alarms. The
cheapest
mobile phone plan I can find is $10 for 33mins. How can a CS offer a
service like this and remain profitable?
Am I misunderstanding how these devices work? Do CS's get such better
rates
that the average joe consumer for his own mobile phone? Or do the CS's
have
a huge GPRS data plan and all devices share the total calculated
bandwidth?
I'm sure I'm missing something simple, but can't seem to figure it out...
Thanks for the info!
Eric
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