Hydrogels have attracted increasing attention in wearable sensors, but preparing underwater hydrogel sensors with excellent anti-swelling and self-healing properties is still challenging. Herein, an anti-swelling and self-healing hydrogel is prepared by grafting poly(acrylic acid) with hydrophobic lauryl methacrylate, as well as constructing a second network and multiple molecular interactions (abbreviated as PALCF). The introduced hydrophobic long alkyl chains and the increased cross-linking density of the hydrogel result in a swelling ratio of only 0.04% after immersion in water for 15 days. Due to abundant metal coordination and hydrogen bonds, the PALCF hydrogel exhibits a high tensile stress of 0.60 MPa and a self-healing efficiency reaching 96.0% after self-healing at 60 °C for 2 min. Based on the piezoresistive effect, the PALCF hydrogel is directly used as an underwater strain sensor with a high sensitivity (GF = 2.24) to control underwater vehicles for rescue implementation. Furthermore, two self-powered triboelectric nanogenerator sensors with contact and non-contact models are constructed based on PALCF hydrogels for underwater communication, capable of sending out SOS messages and drowning alarms in emergency. The proposed underwater sensors with drowning warning and rescuing functions have the potential for use in drowning prevention, human–machine interfaces, and underwater communication system.