Polar T31 transmitter, size M, heart rate monitor accessory. This is quite old, so it's unknown if it's currently usable. I don't know if it has a battery. Please consider purchasing with the understanding of this. No returns or refunds. Even if it has a battery, it may need to be replaced. I don't know how to use it, so I can't answer any questions, thank you. - Model Name: Polar T31 - Type: Transmitter - Size: M - Brand: Polar ★ Even if it's unused, there may be small stains, scratches, or discoloration due to long-term storage or aging. ★ The purchase date and frequency of use are unknown as it is a used item. ★ This is a used item. There may be overlooked stains or scratches. Please refrain from purchasing if you are nervous or seeking perfection. ★ Significant price reductions will not be made. ★ I will not create a dedicated listing. ★ Everything in the pictures is included. ★ Please refer to the photos for the condition. I have inspected the item, but there may be oversights or areas not fully captured in the photos. Also, although it has been cleaned, there may be fine scratches or stains remaining due to it being a used item. ★ Immediate purchase is possible without comments. The person who purchases it first will be prioritized, even if there are comments in progress. ★ Please refrain from comments asking "How much can you lower the price?". If you want a price reduction, please state your desired price in your comment. I will lower the price within a reasonable range if possible. ★ I will ship as compactly as possible. The packing for shipping may differ from the condition in the photos. Please understand. ★ If there is an initial defect, I will accept returns and refunds if it's before the evaluation. (I cannot respond to junk items, as they are assumed to be broken, so please refrain from purchasing if you do not understand.) Thank you for viewing!