We have installed a network of sea level gauges with -40 km spacing in the Shumagin Islands in order to detect relative vertical motion, in particular, possible crustal motion precursory to an expected major earthquake. This required the development and deployment of a pressure sensor sea level gauge suitable for installation on remote and harsh coastlines. Data are collected in near-real-time via satellite, both in order to exploit fully any precursors that may be observed and to provide continuous information on the status of the instruments. Using Wiener filtering techniques, we have determined conservatively that no relative vertical crustal motion >0.1 m between stations has occurred during 1981--1985. This is consistent with independent geodetic leveling and trilateration data, though evidence exists for more rapid deformation during 1978--1980. The sea level data collected so far have an rms noise level of ~0.04 m after processing; this is limited in part by the pressure sensor and associated electronics. Improved pressure gauges with better long-term stability have recently been installed. A short-baseline tiltmeter operating in a tunnel has demonstrated that suitably designed and located land-based tiltmeters have lower noise level, and hence better precursor detection characteristics than the sea level gauges, at monthly and shorter periods.