## 1 Introduction  
The ability to remotely monitor patient vital signs in real time is a growing area of interest [1]. Portable medical monitoring devices are used in hospitals with short range transmission infrastructure to allow patient sensors to communicate with base-stations. The typical use of such sensors sees them worn by the patient and paired with an aggregating transmitter using either fixed land line services or expensive mobile data transmissions. Sensors can be used in the home or other remote locations for the remote monitoring of non-critical care patients. While sensors and base stations allow a patient to be monitored externally to the hospital environment, it does not allow them to have any real degree of mobility in that the patient is still effectively tethered to the base station and the communications infrastructure. However, in some cases it should have been possible to monitor patients remotely, given the correct sensors and communications infrastructure to allow their status to be regularly checked. The trend within patient monitoring has been to allow the patient more mobility [2]. Home monitoring is one of the possible medical applications of the mobility-aware healthcare systems [3-5]. For people to be able to stay in their home environment and feel secure and live as a normal life as possible is important for recovery. The contemporary and emerging developments in wireless communications and network technologies coupled with advances in ubiquitous and wearable technologies will have a radical impact on future health-care delivery systems. These advances have already made a significant impact on current e-health and telemedical systems. Numerous systems for elderly care [6], epilepsy care [7], and patient monitoring [8] based on mobile phones [9], Wi-Fi [8,10], and wireless sensor networks (WSN) [11] have been developed. Networked systems like these are of great economical benefit for the society as it would reduce health care costs. A system to remotely monitor a patient's blood pressure is described in [11]. The data is transferred to a central monitoring station using a wireless sensor network for display and storage. MEDiSN [12] and SMART [8] focus on monitoring patients waiting in emergency rooms. The network architectures in MEDiSIN are stationary relay nodes deployed to ensure connectivity between a patient worn sensor and a base station. AlarmNet [6] supports the collection of data from mobile and static sensors through a query service. [PERSON] _et al_. [13] discussed the design, deploymentand empirical study of a wireless clinical monitoring system that collects pulse and oxygen saturation readings from patients in general hospital units. It is shown that WBAN based on a low cost wireless sensor network technology could greatly benefit patient monitoring systems in residential environments [14]. In this paper, we develop a multi-tier real-time patient monitoring system architecture that integrates medical sensors, a sensor network, electronic patient records and the Short Message Service (SMS) [15] as a data transfer mechanism to allow remote monitoring of patient physiological status in the homecare conditions and to alert medical personnel when life-threatening events occur. SMS is a flexible and pervasive messaging technology which is almost universally accessible to anyone possessing a mobile telephone of second generation or later lineage. With the ability of SMS to encode data in a number of formats, and the capability to expand the user data segment through concatenated SMS, SMS offers excellent capacity for data transmission and it can be considered suitable for the transmission of discrete data in a variety of applications. In the case of critical data, where delivery failure is simply not an option, SMS is not the ideal choice of carrier medium due to the lack of delivery guarantees and standardiseddelivery receipts supported in the protocol.