Providing hands-on practical education without access to laboratories during the COVID-19 pandemic has required creativity and innovation. In this paper, co-authored by academic staff and students, we describe an at-home mobile phone-based 'spectrophotometer' experiment used in an introductory undergraduate biology course. Using colour picker apps, a smartphone can be used to quantify concentration, which was used to compare the strengths of different brands of tea. The protocol is designed to be low-cost and safe to perform outside of a laboratory. Students used the methods to learn important biochemical methods such as preparing dilutions, constructing calibration curves, normalising data and testing a hypothesis. We reflect on the experience of developing and using the protocol from a staff and student perspective, which highlights the advantages of this approach in terms of student independence and inclusivity. We also suggest alternative experiments that could be performed using the protocol. We encourage biology educators to think creatively about the possibilities for using mobile phones or at-home experiments in their teaching. Our experience suggests that at-home experiments like this protocol will have value even after the pandemic is over, particularly in terms of inclusivity.