SMS-enabled surveys are gaining traction as a rapid, low-cost means of monitoring food security situations as part of early warning systems. However, such surveys run the risk of yielding biased results, given that mobile phones are more prevalent among young, urban and wealthier populations. To assess the suitability of SMS-enabled surveys for food security monitoring, we conducted monthly surveys of 2000 respondents across Uganda over the course of one year. A filtering approach was used to ensure a representative sample. We evaluate the validity of the data by triangulating the responses with high-frequency data from our own face to-face household surveys as well as externally collected phone survey data. The analysis suggests that SMS-based surveys can be a promising tool to measure changes in food security status over time, but they perform less well with regard to measuring the actual food security status. Responses related to the general food situation (rather than dietary diversity, food consumption or market prices) emerged as the most reliable indicator. Using different scenarios, we assess implications of changes in the sample composition and size for the results. Even biased samples, e.g. in terms of gender, location or age, show comparable trends, but a minimum sample size is required to obtain valid results.