Text messaging - Phone home
Text messaging can be a convenient interface to the Home when out and about. One-way messaging, for notification of important events, is easy to implement via third party service providers. All of the UK networks operate some kind of e-mail to SMS gateway, whereby an e-mail sent to dedicated e-mail address is automatically forwarded on to the designated mobile. There are also a number of independent suppliers who offer a similar service, albeit at a cost. The caveat is that both e-mail and SMS can be subject to delays in transit, and there is always the risk that the recipient will be out-of-coverage. For routine monitoring, this is rarely a concern, but it can be an issue for security related notifications. In this case, a service such as Intamac, which interfaces direct to the security panel, may be a better choice.
Another alternative for outgoing SMS messages which is often overlooked is delivery via dial-up modem. All four UK operators offer a "paging gateway" service which allows an ordinary analogue modem to dial up and dispatch a text message under script control. This system performs better than e-mail based services because there is one less moving part in the equation.
Bi-directional messaging offers more potential - allowing, for example, a mobile owner to text his house in advance of returning home to turn the heating up or perhaps remotely reboot a server. It is, unfortunately, correspondingly more complex to implement. Whilst some operators offer text-to-e-mail forwarding in addition to the standard e-mail to text service, in practice this is unwieldy and prone to delays. A more effective mechanism for this kind of control is to connect a GSM modem to a local PC and use this to drive both inbound and outbound messages. This has the advantage of delivering messages instanteously in general, providing access to delivery reports - so the sending PC knows whether or not the notification has arrived at the destination mobile - and can be surprisingly cost-effective.
Three options are available in terms of GSM modem. A dedicated external modem, such as the Siemens M3 module or the Falcom AD2 offer a serial interface akin to a normal analogue modem, are suitable for connection to an external aerial in poor signal areas are are very reliable. These modems are available ex-contract for around £135. A number of manufacturers produce GSM data cards in the PC card format, and these also work well on Win/32 systems. Linux drivers for such cards are often hard to come by, however, and the form factor assumes that you either have a special PC card adapter installed in the PC or have a laptop dedicated to the task. The final option is to use a mobile phone that has data-cable support. In my experience this the least reliable option - the phones I've tried seem to need "rebooting" from time to time.
If you decide on using a GSM modem or phone, it will need a dedicated SIM card. This needn't be prohibitively expensive. Virgin mobile offer a pay-as-you-go service "Virgin EQ", which, unlike other PAYG services doesn't require topping up - charges are collected by direct debit. Incoming SMS messages are free, and outgoing messages are charged at 7.5p. Orange will offer a similar service if you invoke their "Orange Value Plan" option, through which they pledge to match any other operators tarrif.
The final link in the chain is the software to drive a modem or phone based solution. There is a Homeseer plugin available for Nokia phones (unfortunately I don't have a link). The sourceforge SMSLink project provides an excellent driver for Siemens, Falcom and a variety of other GSM modems. And lastly, there is xAP support for the Falcom modem available here from the downloads section. This should also work with the Siemens modem, although I haven't tested it personally.
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