These devices require a GSM SIM card in order to send a text alert or dial a phone number when there is an environment related alarm including temperature and humidity. The trigger alarm condition will depend on the sensors connected to the environment monitoring device.
Network hardware SMS gateways provide one way to send SMS text alerts. An internet-based alternative is to use an email-to-sms portal such as https://aql.com/products/messaging/ who can typically provide up to 300 free text messages. Additional pricing bundles start from around £40 for 1000 SMS (4p per text).
With an AQL Email-to-SMS account, you can set up an SMS phone number distribution list and the email address to activate the list from. On receiving an email alert from an environment monitoring software package such as SensDesk or RoomAlert, the portal account will forward the alert message email via an SMS to your predefined mobile phone numbers.