descolgar - to hang up

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Note added at 7 mins (2009-03-18 14:11:17 GMT)
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or hangs up ...

I'd go for is activated maybe in this case.

Luck.

descolgar is 'to pick up' a telephone. Since this is done via remote computer, I would just say: Whenever an alarm goes off the terminal automatically places a call to the central terminal. (something like that)

descolgar un teléfono= levantar = to pick up. Si el texto indica que el sistema realiza un llamado, no puede ser "hang up" o colgar.

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Note added at 27 mins (2009-03-18 14:30:51 GMT)
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I think picks up or connects works with terminal. They are becoming more human every day :)

See the following example from https://www.patentstorm.us/patents/4993059/description.html:

"Whenever an alarm status is generated, the alarm panel 18 seizes the line such that the local telephone 34 is disconnected and goes off-hook for a short period of time to insure that any previous call was disconnected. The alarm panel then goes off-hook to effect a connection with the central office."

You can find many references to "go off-hook" or "goes off-hook" or "seize the line" or "seizes a line" in connection with remote alarms.

Here is another, found at http://www.freepatentsonline.com/EP0566242.html:

Currently there are many applications wherein customer premises equipment of an end user of telemetry service initiates a remote telemetry telecommunications call to some centralized service bureau. Such arrangements are used, for example, to transmit a meter reading, report energy and appliance usage, report alarm or maintenance conditions or to forward burglar alarm signals or fire alarm signals from homes to service bureaus or directly to police or fire stations. In such systems when an alarm indication is detected, a call is automatically set up to the service bureau and some identification of the caller is transmitted over the connection to the service bureau. ... With today's inbound techniques, the Meter Interface Communications Circuit (MICC) (FIG. 1, block 46) dials directly through the central office switch 21 to a central office service unit connected to the utility or third party service provider. ... Calls to the utility, from the central office service unit, can be delivered by a circuit switched network, packet network, or can be further directed by switch based Multiline Hunt Groups or by an Automatic Call Distributor (ACD). The MICC goes off-hook and dials an access code. The switch recognizes the access code and gives a second dial tone.